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THE FIGHT IN THE PALACE

Field, Forest and Farm by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here . ASCENDING SAP CHAPTER XXII. ASCENDING SAP “Now let us see how the plant is nourished by the various substances of which we have just studied the most important. Every form of plant-life is made up, not of a compact and uniform mass of matter with no occasional empty spaces, but, on the contrary, with the aid of a microscope it is seen that an infinite number of very minute cavities called cells are interspersed throughout the body of the plant. These cells may be regarded as extremely small closed sacs, sometimes round, sometimes oval, but more often with irregular and angular outlines by reason of the mutual pressure exerted by the cells. The cell-wall is composed of an excessively fine membrane. In the pith of the elder, all riddled like a sponge, you have an example of cells large enough to be seen without a microscope. Other cavities are long, pointed at both ends and swollen in the middle like a spindle. They are called fibers. Still others form canals of uniform size throughout, as fine as a hair and long enough to extend from the roots to the topmost leaves. These canals are called ducts. Look closely at the cross-section of a very dry vine-branch, and you will see a multitude of orifices into which it would be possible to thrust a [ ]hair. Those are the openings into so many broken ducts. Everything in the plant, absolutely everything—root, stalk, wood, bark, leaves, flowers, fruit, seeds, no matter what—is composed of a mass of cells, fibers, and ducts. 108 “That understood, let us consider the root of the plant. In its new parts, at the tip-ends of its finest ramifications, tip-ends that we have called spongioles, it is composed of cells just formed and consequently tender and fitted for absorbing easily the moisture in the soil. Spongioles, then, fill themselves much as sponges would do. That done, conduits offer their services for conveying the liquid to the top of the plant: they are the ducts just referred to, and comparable here to the water-pipes in our own fountains. But if in fountains water runs by its own weight, going from the highest to the lowest point, it is not so with the liquid absorbed by the roots, a liquid running from below upward. What then is the force that makes it ascend? “This force is in the buds or, to speak more correctly, in the leaves. Each leaf is the seat of an active evaporation whose object is to rid the plant of the great quantity of water required for dissolving in the soil and then conveying to the leaves the nutritive substances present in the soil. This evaporation leaves a void in the cells that have given up the evaporated water. But this void is immediately filled from the neighboring cells, which give up their contents and receive in turn the contents of the next lower layers. From cell to cell, from [ ]fiber to fiber, from duct to duct, a similar transfer takes place at points farther and farther away from the evaporating surface, until the tip-ends of the rootlets are reached, where a continuous absorption makes good the loss of moisture by evaporation. The process reminds one somewhat of the working of our pumps, in which the piston leaves behind it a void that is immediately filled by the water in the pipe, which in its turn gets water from the bottom of the well. This liquid which ascends in every plant, absorbed by the spongioles of the rootlets and put in motion by the evaporation from the leaves, is called ascending sap, or crude sap. The sap is called ascending because it passes from below upward, from the roots to the branches; and it is called crude because it has not yet undergone the preparation that will turn it into the nutritive liquid of the plant. Thus we have learned our first lesson, namely: ascending sap is carried especially to those parts of the plant where buds are numerous, where leaves abound; it seeks by preference the ends of the branches, where evaporation is most active. 109 “We know that the surface wood is the newest; it is formed of cells, fibers, and ducts whose cavities are free and whose walls are permeable. The interior wood is older; its cells, fibers, and ducts are encrusted, stopped up, decrepit, out of use. The liquid accordingly makes its way where circulation is possible, and ceases to flow where the passage is obstructed. That is to say, the ascent of the sap takes place through the sap-wood and chiefly through [ ]the outermost layers, or those of most recent formation. Repeated experiment leaves no doubt on this point. When a tree is cut down at the time of the sap’s greatest activity, we find the sap-wood moist and the older wood perfectly dry. Finally, in herbaceous plants the sap ascends through the whole body of the stem. Suspended during the winter on account of the absence of foliage, this ascent of the sap becomes remarkably brisk at the awakening of vegetation. Then it is that fruit-trees shed tears, so to speak, where the pruning-hook has left its mark; or, in other words, the ascending sap oozes from the openings of the severed ducts. These tears are especially noticeable in the grape-vine, where it has recently been trimmed. 110 “Now what would you expect to find in this liquid if you collected some of it as it trickles in the form of tears either from the vine or from a fruit-tree? Many things, doubtless, you will say, since this precious liquid is the prime source of all that the plant contains in itself. If such is your thought, undeceive yourselves: ascending sap is little more than clear water, and often it is very difficult for science to prove beyond a doubt the presence in it of various substances in solution, so minute a fraction of the whole do they compose. Among these substances the most frequent are compounds of potash, of lime, of carbonic acid gas, traces of phosphates, and compounds of nitrogen or ammonia. In short, the liquid from which the plant is to derive its nourishment is the weakest sort of broth, composed of an enormous [ ]quantity of water and a very small proportion of dissolved substances. These inconsiderable substances are the only or almost the only things utilized by the plant; and the water that has collected them in filtering through the soil, and has then carried them from the roots to the leaves through the sap-wood, the water that forms almost the whole of the ascending sap, is destined, as soon as the journey is accomplished, to leave the plant and return as vapor to the atmosphere whence it descended in the form of rain.” 111 About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Jean-Henri Fabre (2022). Field, Forest and Farm. Urbana, Illinois: Project Gutenberg. Retrieved October https://www.gutenberg.org/cache/epub/67813/pg67813-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org , located at https://www.gutenberg.org/policy/license.html.

ASCENDING SAP

In single-page apps that use the Vue Router, it is common to create a path parameter that changes the behavior of a route. A common problem occurs when a user alters the path manually in the address bar. Manually changing the URL does rerender the view! This can cause unexpected behavior because hooks don't fire and nested components don't reload. not mounted() How to Fix It The solution is to use another hook, . Let's take the example of the . The last parameter in the Playground's path is the code language, or . If the boilerplate code were only fetched using a hook, then when a user changed the path parameter the boilerplate code wouldn't reload. beforeRouteUpdate() Qvault Playground "js" "go" mounted() The reason that it reload is that the Qvault SPA also has the following hook: does beforeRouteUpdate() beforeRouteUpdate (to, , next) { .lang = to.params.lang; .setCode();
  next();
} from this this According to the , the hook receives three parameters: docs : the target being navigated to. 1. to Route Object : the current route being navigated away from. 2. from : this function must be called to the hook. The action depends on the arguments provided to next: 3. next resolve : move on to the next hook in the pipeline. If no hooks are left, the navigation is . next() confirmed : abort the current navigation. If the browser URL was changed (either manually by the user or via back button), it will be reset to that of the from route. next(false) : redirect to a different location. The current navigation will be aborted and a new one will be started. You can pass any location object to next, which allows you to specify options like replace: true, name: 'home' and any option used in or next('/') or next({ path: '/' }) router-link's to prop router.push : (2.4.0+) if the argument passed to next is an instance of Error, the navigation will be aborted and the error will be passed to callbacks registered via . next(error) router.onError() In the case of the Qvault Playground, we are just doing the same operation that the hook does: we check the language and fetch the boiler plate. mounted() What If I Want All Routes To Update? If this is a common problem in your app, you can set your entire to re-render when its path changes by providing a key property: router-view < = /> router-view :key "$route.fullPath" With the above, you won't need to use the hook, and can directly access the now-reactive property. The only problem with this method is that every path in that router will update in the case of a path change. You may not want all that needless re-rendering, but that's a decision for you to make. beforeRouteUpdate() this.$route.params.myVar Thanks For Reading Follow us on Twitter if you have any questions or comments @q_vault Take game-like coding courses on Qvault Classroom to our Newsletter for more educational articles Subscribe Previously published at https://qvault.io/2020/07/07/how-to-rerender-a-vue-route-when-path-parameters-change/

An Essential Guide to Re-rendering Vue Routes When Path Parameters Change

Writing apps can be hard. Writing apps that are free from bugs is nigh on impossible. Explicit types can help, but unless you are talking about using an exotic language like , or other , then having types is not enough, by itself, to keep our safe from exceptions at runtime. Some effort has to go into the programmer’s work, to help the compiler out, because there are going to be some blind spots. With that said, not all independently-typed languages are equal; a Haskell or a or an Elm is going to do a much better job at preventing runtime errors than, say, C, due to the checks and the available to the compiler and the . Agda Dependently Typed languages systems PureScript tools developer Where is the power coming from, in these more exotic lands? How can we take advantage of some of the same concepts in some of the more common languages in the day-to-day of working for companies that are a little less bleeding-edge? One of the reasons that the Elm authors and adopters claim that it runs without runtime errors, and “if it compiles, it probably works”, is due to living in a . Closed System But what does that even mean? — S.Traumann Great timing, tired narrative helper! Glad you asked. A Finite State Machine representing a coin allowing a turnstile to unlock. Credit: Wikimedia Commons This is a Finite State Machine which describes the constraints and the behaviours of a coin-operated turnstile. If you squint, you can also apply that machine to gumball machines, or cheap vending machines, or really a lot of things, by scribbling out some words and replacing them. This is (hopefully) a . We know all of the behaviours. We know all of the dependencies. We know the shape, size and value of the coin or token that the machine is willing to accept. We can always figure out what state we should be in, and where we should go, based on where we are and what we have. It’s for amusement parks and transit systems. Closed System Zork If we add more potential states, it gets more complex to work with, but it can still be a closed system as long as you can clearly define all valid transitions between all states. I’m going to avoid talking about structuring applications via FSM, for now. Instead, I’m going to argue that the part that we tend to have the most problems with in our applications is the . coin Rather than a turnstile, allow me to try to illustrate with an app that ought to function like a gumball machine: put a token in, and based on the value of the token, you get the equivalent in candy. There’s not a whole lot going on. If you give me a token worth 2, I give you 2 candies. If you give me a token worth 5, I give you 5 candies. The compiler is happy, the QAs are happy with the desk checks… all that is left is to hook it up to the online token service, and it’s ready to go out into the wild. Well… first, there are a lot of complaints that the system has eaten the user’s money, without delivering anything. Those have been followed by reports that people might be gaming the system, and running off with candy that doesn’t fit neatly into the amounts the system is designed to work with. How could either of those things possibly happen? The compiler said everything was great!…but the compiler isn’t running at runtime, and didn’t take the type-safety of the entire internet (ie: none) into account, when it was compiling. You do a little digging into ; turns out, if anything goes wrong when handling the payment, the token ends up being returned as . It also appears that it’s possible to get a token worth 7, based on some outdated requirements, and a token value of 10.2, due to a weird gap in the logic with the exchange rate. **processTransaction** **null** We know how to fix all of those. No more exceptions! We handle the null case, we check that the token value is an integer… and if we can’t make it work the way it’s supposed to, we just return and made a quick change to the return type to support having no value. Done! Wrap it up and go home. **undefined** …but did we really solve the problem, though? We solved the code that was crashing in our service. We solved cases where people might be cheating the system. But did we solve the problem of users’ money disappearing with no candy in return? really Nope. Not even a little. In fact, the people who were buying 7 pieces earlier would have been receiving 7 pieces from our service. Those people are still paying money, but all they are being delivered is . **undefined** What can we do about it, then? If we can’t go overboard checking that the token is valid inside of the service, how do we make sure it’s working correctly? Well, that’s just it. The service is a closed system; or it used to be. In order to do its job perfectly, it expected to receive a valid token, and to return a valid set of candy. As soon as you send a dubious token through, the whole codebase is at risk of being clogged with checks and casting that will only add confusion, and returning values which will only serve to break the next person in line, with no context of the problem you had. If that starts getting hairy inside of 8 lines of code, think about how scary a 140,000 line long app might be. In order to close that system back up, you need to identify all possible paths, to transition from one state to the other. In other words, you need to know all possible permutations of all possible loops and branches, so you can ensure that all possible exits from your state are known, and valid. The easiest way to ensure that is to ensure that only valid data enters your system. Let me say that one more time:The easiest way to ensure that you are working in a correct system, or even have the ability to ensure that it can ever be correct, is to ensure that only valid data ever enters your system, and all invalid input is rejected before you do anything else. Those few lines do a better job of fixing your app’s behaviour than all the if/else checks you could possibly care to add, on the inside. Checking here, instead, leaves you better informed about what to do in the case the token is missing, malformed, or otherwise ill-suited for the job. If you’ve ever played a quarter-fed arcade machine, take note that they don’t check the quarter’s validity while you are pushing the jump button, or moving the joystick (regardless of how much it might feel that way); they check it before they ever let you hit the start button. And if it is invalid in a way that is recoverable, they will throw your bad input out the coin-return for you to try again. Bubbles in a fluid line. Gaps in a seal. These are things which need to be checked and prevented at the boundary, because letting bad input in can wreak major havoc once inside the system, whether we’re talking about bloodstreams or brake lines, concrete or space suits. Why is code different? It’s not; that question was rhetorical. Next time, I’m going to take a swing at outlining some of the biggest contributors to bad input at boundaries, and try to offer safe and efficient methods for dealing with it.

A Closed System is a Happy System

The Beautiful and Damned: Book III, Chapter II - A Matter of Aesthetics

Social Life in the Insect World by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here . THE MANTIS.—THE CHASE CHAPTER V. THE MANTIS.—THE CHASE There is another creature of the Midi which is quite as curious and interesting as the Cigale, but much less famous, as it is voiceless. If Providence had provided it with cymbals, which are a prime element of popularity, it would soon have eclipsed the renown of the celebrated singer, so strange is its shape, and so peculiar its manners. It is called by the Provençals lou Prègo-Diéu, the creature which prays to God. Its official name is the Praying Mantis (Mantis religiosa, Lin.). For once the language of science and the vocabulary of the peasant agree. Both represent the Mantis as a priestess delivering oracles, or an ascetic in a mystic ecstasy. The comparison is a matter of antiquity. The ancient Greeks called the insect Μἁντιϛ, the divine, the prophet. The worker in the fields is never slow in perceiving analogies; he will always generously supplement the vagueness of the facts. He has seen, on the sun-burned herbage of the meadows, an insect of commanding appearance, drawn up in majestic attitude. He has noticed its wide, delicate wings of green, trailing behind it like long linen veils; he has seen its fore-limbs, its arms, so to speak, raised towards to the sky in a gesture of invocation. This was enough: popular imagination has done the rest; so that since the period of classical antiquity the bushes have been peopled with priestesses emitting oracles and nuns in prayer. Good people, how very far astray your childlike simplicity has led you! These attitudes of prayer conceal the most atrocious habits; these supplicating arms are lethal weapons; these fingers tell no rosaries, but help to exterminate the unfortunate passer-by. It is an exception that we should never look for in the vegetarian family of the Orthoptera, but the Mantis lives exclusively upon living prey. It is the tiger of the peaceful insect peoples; the ogre in ambush which demands a tribute of living flesh. If it only had sufficient strength its blood-thirsty appetites, and its horrible perfection of concealment would make it the terror of the countryside. The Prègo-Diéu would become a Satanic vampire. Apart from its lethal weapon the Mantis has nothing about it to inspire apprehension. It does not lack a certain appearance of graciousness, with its slender body, its elegant waist-line, its tender green colouring, and its long gauzy wings. No ferocious jaws, opening like shears; on the contrary, a fine pointed muzzle which seems to be made for billing and cooing. Thanks to a flexible neck, set freely upon the thorax, the head can turn to right or left as on a pivot, bow, or raise itself high in the air. Alone among insects, the Mantis is able to direct its gaze; it inspects and examines; it has almost a physiognomy. There is a very great contrast between the body as a whole, which has a perfectly peaceable aspect, and the murderous fore-limbs. The haunch of the fore-limb is unusually long and powerful. Its object is to throw forward the living trap which does not wait for the victim, but goes in search of it. The snare is embellished with a certain amount of ornamentation. On the inner face the base of the haunch is decorated with a pretty black spot relieved by smaller spots of white, and a few rows of fine pearly spots complete the ornamentation. The thigh, still longer, like a flattened spindle, carries on the forward half of the lower face a double row of steely spines. The innermost row contains a dozen, alternately long and black and short and green. This alternation of unequal lengths makes the weapon more effectual for holding. The outer row is simpler, having only four teeth. Finally, three needle-like spikes, the longest of all, rise behind the double series of spikes. In short, the thigh is a saw with two parallel edges, separated by a groove in which the foreleg lies when folded. The foreleg, which is attached to the thigh by a very flexible articulation, is also a double-edged saw, but the teeth are smaller, more numerous, and closer than those of the thigh. It terminates in a strong hook, the point of which is as sharp as the finest needle: a hook which is fluted underneath and has a double blade like a pruning-knife. A weapon admirably adapted for piercing and tearing, this hook has sometimes left me with visible remembrances. Caught in turn by the creature which I had just captured, and not having both hands free, I have often been obliged to get a second person to free me from my tenacious captive! To free oneself by violence without disengaging the firmly implanted talons would result in lacerations such as the thorns of a rosebush will produce. None of our insects is so inconvenient to handle. The Mantis digs its knife-blades into your flesh, pierces you with its needles, seizes you as in a vice, and renders self-defence almost impossible if, wishing to take your quarry alive, you refrain from crushing it out of existence. When the Mantis is in repose its weapons are folded and pressed against the thorax, and are perfectly inoffensive in appearance. The insect is apparently praying. But let a victim come within reach, and the attitude of prayer is promptly abandoned. Suddenly unfolded, the three long joints of the deadly fore-limbs shoot out their terminal talons, which strike the victim and drag it backwards between the two saw-blades of the thighs. The vice closes with a movement like that of the forearm upon the upper arm, and all is over; crickets, grasshoppers, and even more powerful insects, once seized in this trap with its four rows of teeth, are lost irreparably. Their frantic struggles will never release the hold of this terrible engine of destruction. The habits of the Mantis cannot be continuously studied in the freedom of the fields; the insect must be domesticated. There is no difficulty here; the Mantis is quite indifferent to imprisonment under glass, provided it is well fed. Offer it a tasty diet, feed it daily, and it will feel but little regret for its native thickets. For cages I use a dozen large covers of wire gauze, such as are used in the larder to protect meat from the flies. Each rests upon a tray full of sand. A dry tuft of thyme and a flat stone on which the eggs may be laid later on complete the furnishing of such a dwelling. These cages are placed in a row on the large table in my entomological laboratory, where the sun shines on them during the greater part of the day. There I install my captives; some singly, some in groups. It is in the latter half of August that I begin to meet with the adult insect on the faded herbage and the brambles at the roadside. The females, whose bellies are already swollen, are more numerous every day. Their slender companions, on the other hand, are somewhat rare, and I often have some trouble in completing my couples; whose relations will finally be terminated by a tragic consummation. But we will reserve these amenities for a later time, and will consider the females first. They are tremendous eaters, so that their entertainment, when it lasts for some months is not without difficulties. Their provisions must be renewed every day, for the greater part are disdainfully tasted and thrown a side. On its native bushes I trust the Mantis is more economical. Game is not too abundant, so that she doubtless devours her prey to the last atom; but in my cages it is always at hand. Often, after a few mouthfuls, the insect will drop the juicy morsel without displaying any further interest in it. Such is the ennui of captivity! To provide them with a luxurious table I have to call in assistants. Two or three of the juvenile unemployed of my neighbourhood, bribed by slices of bread and jam or of melon, search morning and evening on the neighbouring lawns, where they fill their game-bags, little cases made from sections of reeds, with living grasshoppers and crickets. On my own part, I make a daily tour of the paddock, net in hand, with the object of obtaining some choice dish for my guests. These particular captures are destined to show me just how far the vigour and audacity of the Mantis will lead it. They include the large grey cricket (Pachytylus cinerascens, Fab.), which is larger than the creature which devours it; the white-faced Decticus, armed with powerful mandibles from which it is wise to guard one's fingers; the grotesque Truxalis, wearing a pyramidal mitre on its head; and the Ephippigera of the vineyards, which clashes its cymbals and carries a sabre at the end of its barrel-shaped abdomen. To this assortment of disobliging creatures let us add two horrors: the silky Epeirus, whose disc-shaped scalloped abdomen is as big as a shilling, and the crowned Epeirus, which is horribly hairy and corpulent. I cannot doubt that the Mantis attacks such adversaries in a state of nature when I see it, under my wire-gauze covers, boldly give battle to whatever is placed before it. Lying in wait among the bushes it must profit by the prizes bestowed upon it by hazard, as in its cage it profits by the wealth of diet due to my generosity. The hunting of such big game as I offer, which is full of danger, must form part of the creature's usual life, though it may be only an occasional pastime, perhaps to the great regret of the Mantis. Crickets of all kinds, butterflies, bees, large flies of many species, and other insects of moderate size: such is the prey that we habitually find in the embrace of the murderous arms of the Mantis. But in my cages I have never known the audacious huntress to recoil before any other insect. Grey cricket, Decticus, Epeirus or Truxalis, sooner or later all are harpooned, held motionless between the saw-edges of the arms, and deliciously crunched at leisure. The process deserves a detailed description. At the sight of a great cricket, which thoughtlessly approaches along the wire-work of the cover, the Mantis, shaken by a convulsive start, suddenly assumes a most terrifying posture. An electric shock would not produce a more immediate result. The transition is so sudden, the mimicry so threatening, that the unaccustomed observer will draw back his hand, as though at some unknown danger. Seasoned as I am, I myself must confess to being startled on occasions when my thoughts have been elsewhere. The creature spreads out like a fan actuated by a spring, or a fantastic Jack-in-the-box. The wing-covers open, and are thrust obliquely aside; the wings spring to their full width, standing up like parallel screens of transparent gauze, forming a pyramidal prominence which dominates the back; the end of the abdomen curls upward s crosier-wise, then falls and unbends itself with a sort of swishing noise, a pouf! pouf! like the sound emitted by the feathers of a strutting turkey-cock. One is reminded of the puffing of a startled adder. Proudly straddling on its four hind-claws, the insect holds its long body almost vertical. The murderous fore-limbs, at first folded and pressed against one another on the thorax, open to their full extent, forming a cross with the body, and exhibiting the axillæ ornamented with rows of pearls, and a black spot with a central point of white. These two eyes, faintly recalling those of the peacock's tail, and the fine ebony embossments, are part of the blazonry of conflict, concealed upon ordinary occasions. Their jewels are only assumed when they make themselves terrible and superb for battle. Motionless in its weird position, the Mantis surveys the acridian, its gaze fixed upon it, its head turning gently as on a pivot as the other changes place. The object of this mimicry seems evident; the Mantis wishes to terrorise its powerful prey, to paralyse it with fright; for if not demoralised by fear the quarry might prove too dangerous. Does it really terrify its prey? Under the shining head of the Decticus, behind the long face of the cricket, who is to say what is passing? No sign of emotion can reveal itself upon these immovable masks. Yet it seems certain that the threatened creature is aware of its danger. It sees, springing up before it, a terrible spectral form with talons outstretched, ready to fall upon it; it feels itself face to face with death, and fails to flee while yet there is time. The creature that excels in leaping, and might so easily escape from the threatening claws, the wonderful jumper with the prodigious thighs, remains crouching stupidly in its place, or even approaches the enemy with deliberate steps. [2] It is said that young birds, paralysed with terror by the gaping mouth of a serpent, or fascinated by its gaze, will allow themselves to be snatched from the nest, incapable of movement. The cricket will often behave in almost the same way. Once within reach of the enchantress, the grappling-hooks are thrown, the fangs strike, the double saws close together and hold the victim in a vice. Vainly the captive struggles; his mandibles chew the air, his desperate kicks meet with no resistance. He has met with his fate. The Mantis refolds her wings, the standard of battle; she resumes her normal pose, and the meal commences. In attacking the Truxalis and the Ephippigera, less dangerous game than the grey cricket and the Decticus, the spectral pose is less imposing and of shorter duration. It is often enough to throw forward the talons; this is so in the case of the Epeirus, which is seized by the middle of the body, without a thought of its venomous claws. With the smaller crickets, which are the customary diet in my cages as at liberty, the Mantis rarely employs her means of intimidation; she merely seizes the heedless passer-by as she lies in wait. When the insect to be captured may present some serious resistance, the Mantis is thus equipped with a pose which terrifies or perplexes, fascinates or absorbs the prey, while it enables her talons to strike with greater certainty. Her gins close on a demoralised victim, incapable of or unready for defence. She freezes the quarry with fear or amazement by suddenly assuming the attitude of a spectre. The wings play an important part in this fantastic pose. They are very wide, green on the outer edge, but colourless and transparent elsewhere. Numerous nervures, spreading out fan-wise, cross them in the direction of their length. Others, transversal but finer, cut the first at right angles, forming with them a multitude of meshes. In the spectral attitude the wings are outspread and erected in two parallel planes which are almost in contact, like the wings of butterflies in repose. Between the two the end of the abdomen rapidly curls and uncurls. From the rubbing of the belly against the network of nervures proceeds the species of puffing sound which I have compared to the hissing of an adder in a posture of defence. To imitate this curious sound it is enough rapidly to stroke the upper face of an outstretched wing with the tip of the finger-nail. In a moment of hunger, after a fast of some days, the large grey cricket, which is as large as the Mantis or larger, will be entirely consumed with the exception of the wings, which are too dry. Two hours are sufficient for the completion of this enormous meal. Such an orgy is rare. I have witnessed it two or three times, always asking myself where the gluttonous creature found room for so much food, and how it contrived to reverse in its own favour the axiom that the content is less than that which contains it. I can only admire the privileges of a stomach in which matter is digested immediately upon entrance, dissolved and made away with. The usual diet of the Mantis under my wire cages consists of crickets of different species and varying greatly in size. It is interesting to watch the Mantis nibbling at its cricket, which it holds in the vice formed by its murderous fore-limbs. In spite of the fine-pointed muzzle, which hardly seems made for such ferocity, the entire insect disappears excepting the wings, of which only the base, which is slightly fleshy, is consumed. Legs, claws, horny integuments, all else is eaten. Sometimes the great hinder thigh is seized by the knuckle, carried to the mouth, tasted, and crunched with a little air of satisfaction. The swollen thigh of the cricket might well be a choice "cut" for the Mantis, as a leg of lamb is for us! The attack on the victim begins at the back of the neck or base of the head. While one of the murderous talons holds the quarry gripped by the middle of the body, the other presses the head downwards, so that the articulation between the back and the neck is stretched and opens slightly. The snout of the Mantis gnaws and burrows into this undefended spot with a certain persistence, and a large wound is opened in the neck. At the lesion of the cephalic ganglions the struggles of the cricket grow less, and the victim becomes a motionless corpse. Thence, unrestricted in its movements, this beast of prey chooses its mouthfuls at leisure. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Jean-Henri Fabre (2006). Social Life in the Insect World. Urbana, Illinois: Project Gutenberg. Retrieved October https://www.gutenberg.org/cache/epub/18350/pg18350-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org , located at https://www.gutenberg.org/policy/license.html .

THE MANTIS.—THE CHASE

React v16.8.0 has been released, which means that React Hooks are now available in a stable release of React. This is something I’ve been looking forward to, ever since I first started playing around with hooks in the alpha releases. I believe hooks are going to bring about a sea change in the way React components are written, and composed, and this is a change for the better. If you have not yet heard of React hooks, you should probably go read , on the React documentation site. Following that you might also want to read this excellent by Dan Abramov. this overview on hooks article on hooks Beware: Here there be Magic! I’ve been talking about hooks a lot recently, and a lot of times, somebody points out that while hooks seem to be a great solution to the problem of composing side-effects, and state management in our React components, it also appears to be a bit of a black box, with unidentifiable magic happening to get it to actually work. Most of these people justified their claims of hooks being magic due to: Hooks requiring to be called in the same static order during every render. Hooks can only be called from within other hooks or function components. The hook appears to track the of the component, which was never passed to it. useState state While magic might be fun if you’re at a show, it certainly is not fun when you’re writing software, and for the life of you, cannot figure out why your library is doing something weird, unexpected, and defying all logic. So let’s deconstruct the magic, and see what exactly is happening behind the scenes in each of these cases. Let the UnMagicking Begin! Hooks require to be called in the same static order during every render. The first factor that people notice is that (as mentioned in the ), hooks are very fussy about their call order. Specifically, React mandates that on every render, the order in which the hooks are called must be the same. This means that you can not call hooks inside loops or conditions, and instead they have to be called at the top-most level. Rules for Hooks The reason behind this is quite simple. Consider a few hooks defined in a function component like this: const [firstName, setFirstName] = useState('John'); const [lastName, setLastName] = useState('Doe');const [age, setAge] = useState(28); As you can see, this is a plain ES6 call to a function called . The only information that the function ever gets is the initial value that is passed into it (well not exactly, but we'll get back to that later). The call then returns an array in the form of . useState useState setState [value, setter] On subsequent renders, the same method will return the updated state value for that particular property. In order to do this, the method will have to somehow keep track of each property requested. However, there is absolutely no place where we are passing a of any sort to the method. useState useState key useState So how exactly does know what state to return for which call? Well uses the call sequence number inside the render function to track the state. So in the above example the first call to will always return the value of and it's setter, the second call will always return the value of and it's setter and so on and so forth. useState useState useState firstName lastName If like me, you are probably thinking that there would have to have been a much better way to implement this, instead of relying on call order, which seems quite hacky. Sebastian Markbage left an on the React Hooks RFC, addressing that amongst other things. You should probably go read that too. excellent comment Anyway, the short of it is that if you’re using hooks, you absolutely must call the hooks in the same order on every render, or Bad Things Will Happen, with React thinking you want to get or set a certain state value, when the one you want is entirely different. An easy way to understand this is to think of as maintaining a key-value map linking the call order to the state value. On the first render, initializes the key-value map as: useState useState const [firstName, setFirstName] = useState('John'); // internal state: {0: 'John'}const [lastName, setLastName] = useState('Doe'); // internal state: {0: 'John', 1: 'Doe'}const [age, setAge] = useState(28); // internal state: {0: 'John', 1: 'Doe', 2: 28} On the second render, already has a key-value map, so instead of setting values on it, it just retreives the values based on the call order. Please note, does not actually maintain a simple key-value map, and the actual implementation is a bit more complicated than that. But for the purpose of understanding why the call order matters, you can think of it as effectively being a key-value map. useState useState Hooks can only be called from within other hooks or function components. Another big rule of hooks, is that you can only ever call a hook from a React function component, or from within other hooks. If you think about it, this makes complete sense — if your hook is going to have to get or set the state of a component, or trigger side-effects, either directly or indirectly, then it needs to be linked to a specific React component, to which that state would belong. Otherwise, how would React know which component’s state your hook is trying to access? So far all seems good. There’s nothing really magicky about this one is there? Well if you want to see the magic, you need to break this rule, and call a hook from inside a normal Javascript function. function catchMeIfYouCan(){     const [firstName, setFirstName] = useState('John'); }; Running this code immediately throws an error: Uncaught Error: Hooks can only be called inside the body of a function component. Now hold on a minute! If the call is just a normal function call, and a function in Javascript can't really do much in the way of analyzing the method that called it, how did React know that the method was being called from outside a React component? Magic? Not really, but since this ties into the next magicky item on our list, I'll address them both together. useState useState The hook appears to track the of the component, which was never passed to it. useState state Consider two components and , both of which have the state properties , and . Student Teacher firstName lastName age class StudentComponent extends React.Component{constructor(props){super(props);this.state = {firstName: 'Bobby',lastName: 'Tables',age: 8}}render(){return <div>{this.state.firstName} {this.state.lastName} ({this.state.age})</div>}} class TeacherComponent extends React.Component{constructor(props){super(props);this.state = {firstName: 'John',lastName: 'Keating',age: 34}}render(){return <div>{this.state.firstName} {this.state.lastName} ({this.state.age})</div>}} In the above example, in both of the components, is an instance property, and therefore can be accessed from within any of the class methods. Since it is an instance property and not a commonly shared object, the values are also encapsulated correctly and cannot access the state of and vice-versa. state TeacherComponent StudentComponent Now let’s convert these components into their function component counterparts using the hook. useState function StudentComponent(props){const [firstName, setFirstName] = useState('Bobby');const [lastName, setLastName] = useState('Tables');const [age, setAge] = useState(8); return <div>{firstName} {lastName} ({age})</div> }; function TeacherComponent(props){const [firstName, setFirstName] = useState('John');const [lastName, setLastName] = useState('Keating');const [age, setAge] = useState(34); return <div>{firstName} {lastName} ({age})</div> }; If you notice here, in both of the components, we are calling the same method, which is a method imported from the React library, and commonly shared amongst both the components. Like we discussed earlier, uses only the call order to keep track of the state values. useState useState Given this, if we render first, setting the , and state properties, and then render immediately after it, then the should be able to access the state values set by the right? StudentComponent firstName lastName age TeacherComponent TeacherComponent StudentComponent Well actually no. Even whilst using hooks, React ensures that the values are always properly encapsulated, and cannot be accessed by the wrong component. Otherwise, life wouldn't exactly be pleasant, with every component being able to access the state of all other components, would it? state But given that we are no longer using to encapsulate the state within an instance of a component, how can React perform this encapsulation for us? The answer to that is actually quite simple. But before we get to it, we need to make a slight detour into the internals of React. Or rather, the internals of React-DOM. this Better Rendering Performance with React Fiber In the initial versions of React, rendering components was something that happened as a single continuous action. In a React application, a change to the state of the application triggers a re-rendering of the entire application. However, in practice, for any non-trivial application, re-rendering the entire application results in terrible performance. In order to improve the performance, React performs quite a few optimizations. Most of these optimizations occur during the stage. Reconciliation is basically the process by which React synchronizes the Virtual DOM that it has built up by executing the methods on each component instance, with the actual DOM that is constructed on the browser. Reconciliation render Prior to React Fiber (released in v16 of React), React relied on call stack to manage rendering. Whenever a component had to be re-rendered it was added to the call stack, and once the other items on the stack finished rendering, this component would render. However, while there were items on the stack, no other work could be done. Rendering would block all other functions, and rendering could not be broken up into smaller chunks and run. In order to tackle this issue, Fiber was introduced. Fiber is basically a custom re-implementation of the call stack, which allows for things like splitting a big task into smaller work units, pausing and resuming these work units as required, as well as dropping the work units if they were no longer required. In order to achieve this, Fiber internally references each instance of a React component as a ‘fiber’ object. The fiber object is a JavaScript object that contains information about a component, its input, and its output. It is analogous to a stack frame, but it also corresponds to an instance of a component. What this effectively means is that each instance of a component is internally represented in React as a ‘fiber’, and these fibers have a lot of properties that are used by React to keep track of things like and . state props So what does all this have to do with encapsulating the in function components? state Well each component instance is a fiber, and fibers have a lot of internal React-specific properties. In both the class component and the function component, the actual instance of the component is represented as a fiber, that is not accessible outside of React internals. When we call in our class component, rather than immediately merge the partial state into the pre-existing state, Fiber will create an updateAction and enqueue that action. The queue upon which the action is enqueued is specific to each individual fiber, and most actions that are to be performed on a fiber, are enqueued rather than directly run. Enqueueing the actions allows Fiber to schedule and control the execution. this.setState The exact same thing happens when we call hook in a function component, or when we use the setter method returned by the hook. The corresponding action to be performed is enqueued on the fiber that represents this specific instance of the component. useState useState The only difference between the class component and the function component, is how the specific fiber corresponding to a particular component instance is identified. In the class component, the class component instance itself has a property which directly gives the corresponding fiber. This is set by React when the component is initially constructed. _reactInternalFiber However, in the function component, there exists no such key. So going back to our example: function StudentComponent(props){const [firstName, setFirstName] = useState('Bobby');const [lastName, setLastName] = useState('Tables');const [age, setAge] = useState(8); return <div>{firstName} {lastName} ({age})</div> }; function TeacherComponent(props){const [firstName, setFirstName] = useState('John');const [lastName, setLastName] = useState('Keating');const [age, setAge] = useState(34); return <div>{firstName} {lastName} ({age})</div> }; How does React encapsulate the data between the two component instances? By now, we know that the solution involves maintaining individual fibers for each component instance, and this fiber is set when the component is first constructed. But how does know which component is trying to access the state and return the appropriate state? useState Well, the solution that React uses to identify the calling component instances is extremely simple. In React, at any given point in time, there can be only one component that is currently rendering. React also knows exactly when a component render starts, and when it ends. So when a component instance is about to start rendering React sets a flag , pointing to that instance. When the component is done rendering, the flag is nulled. currentlyRenderingFiber Since a hook function can only be called from within a function component, and function components are basically just the render methods of the class components, it is guaranteed that whenever a hook is called, we will be in the middle of a render, and will be pointing to the fiber that is being rendered. The of the component instance is maintained as a property on this fiber, and that is what uses to get the state for the correct component instance. currentlyRenderingFiber state useState Remember, that error we saw earlier when a hook was called from a normal Javascript function? Uncaught Error: Hooks can only be called inside the body of a function component. So how did React know this was not called from within a function component? Well, React only sets the , and some other items when the component is rendered as a function component. When you call the hook from a normal javascript object, these items are not set, and that's when React throws the error. currentlyRenderingFiber dispatcher And the magic is dispelled! So that’s basically all there is to all the magic behind React Hooks. Now that we know exactly what’s going on behind the scenes, we should be able to better understand hooks, how they work, and why we need to stick to the peculiar rules for writing hooks. I’d love to hear your opinion on things I’ve written in this post. So do chime in with your comments below. Originally published at asleepysamurai.com .

Deconstructing the Magic Behind React Hooks

Things you should keep in mind. Lets face it, every developer wants to improve and become better. The big question that most developers ask is how will I do it. Here are a list of things you should keep in mind while . programming Code Presentation As any discussion about code layout grows, the probability of it descending into a fruitless argument approaches one. You know the tabs vs spaces, bracket placement weather on new line or the same line. A good code format is not the one you think looks prettiest. A good format is the one that makes it easier to scan and read the code. Good code presentation reveals your code’s intent. It is not an artistic endeavor. We need good presentation to avoid making code errors. Not so we can create pretty ASCII art. We write code to be executed by a computer, but to be read by humans. If any man wishes to write a clear style, let him first be clear in his thoughts. Pick one layout style and use it consistently or adopt coding standard or style guide. If you’re working in a file that doesn’t follow the layout conventions of the rest of your project, follow the layout conventions in that file. Naming A good name is descriptive, correct, and idiomatic. You can only name something well if you know exactly what it is. Make sure you know what it is before giving cryptic names to variables. Avoid redundancy. It shows you didn’t think through the naming of what you are building. Be it a class or function or variables class ItemList { public int numberOfItems () {…} }// numberOfItems is unnecessarily long, repeating the word Item// it could be renamed to size or even length Employ the capitalization conventions most often used in your language. Like in methods are capitalized C# Console.WriteLine("Hello World") Ensure that your names are accurate and avoid spelling mistakes. Never alter presentation and behavior at the same time. Make them separate version-controlled changes. Adapt your presentation style as you gain experience. As a beginner you don’t always start out with good code presentation, your are more concerned about whether the program works or not. Write Less Code Writing lots of code does not mean that you’ve written lots of software. It may just mean you are written lots of bugs. More code means there is more to read and more to understand — it makes our programs harder to comprehend. The more code you have, the more places there are for bugs to hide and tracking them down may not be that easy. Avoid Unnecessary Code Common class of pointless code is the unnecessary use of conditional statements and tautological logic constructs. Flappy logic is the sign of a flappy mind. // exampleif (expresion) {return true;} else {return false;}// which can be refactored toreturn expresion; Express code clearly and succinctly. Avoid unnecessarily long winded statements. They don’t add any value to your code. Duplication Do not copy code sections. Factor them into a common function. Use parameters to express any differences. If you spot duplication, remove it. Dead Code Dead code is code that is never run, that can never be reached. Tell your code to get a life, or get lost. Other manifestations of dead code include: Functions that are never called Variables that are written but never read Parameters passed to an internal method that are never used Enums, structs, classes, or interfaces that are never used Comments Good code does not need reams of comments to prop it up, or to explain how it works. Make sure that every comment adds value to the code. The code itself says what and how. A comment should explain why — but only if it’s not already clear. Do not remove code by commenting it out. It confuses the reader and gets in the way. Every day, leave your code a little better than it was. Remove redundancy and duplication as you find it. Improve Code by Removing It You can improve a system by adding new code. You can also improve a system by removing code. How dead code spring up during development Features are removed from an application’s user interface, but the backend support code is left in. Wizard-generated UI code inserts hooks that are frequently never used. Remove dead code wherever possible. It gets in the way and slows you down. It is safe to remove code that you might need in the . You can always get it back from version control. future Code cleanup should always be made in separate commits to functional changes. Dead code happens in even the best codebases. Be wary of the Past You thought it was perfect when you wrote it, but cast a critical eye over your old code and you’ll inevitably bring to light all manner of code gotchas. Looking back at your older code will inform you about the improvement (or otherwise) in your coding skills. How to go about an existing codebase Coming into any large existing codebase is hard. You have to rapidly: Discover where to start looking at the code Work out what each section of the code does, and how it achieves it Gauge the quality of the code Work out how to navigate around the system Understand the coding idioms, so your changes will fit in sympathetically Find the likely location of any functionality (and the consequent bugs caused by it) Your best route into code is to be led by someone who already knows the terrain. Don’t be afraid to ask for help! The best way to learn code is to modify it. Then learn from your mistakes. Many programmers, rather than putting in the effort to read and understand existing code, prefer to say “it’s ugly” and rewrite it. Be prepared to encounter bad code. Fill your toolbox with sharp tools to deal with it. Some filthy code was simply written by a less capable programmer. Or by a capable programmer on a bad day. Silence the feeling of revulsion when you encounter “bad” code. Instead, look for ways to practically improve it. You can’t expect any code, even your own, to be perfect. Follow the Boy Scout Rule. Whenever you touch some code leave it better than you found it. Make code changes slowly, and carefully. Make one change at a time. Dealing with Errors Do not ignore possible errors in your code. Don’t put off handling errors until “later” (you won’t get around to it). Use exceptions well, with discipline. Understand your language’s idioms and requirements for effective exception use. Programmers must be made aware of programmatic errors. Users must be made aware of usage errors. It’s not good enough to log the error (somewhere), and hope that a diligent operator will notice an error and do something about it one day. Be prepared for the Unexpected At every step, consider all of the unusual things that might occur, no matter how unlikely you think they’ll be. Always consider errors that you can recover from, and write appropriate recovery code. Ensure that your error handling is idiomatic, and uses the appropriate language mechanisms. Consider all potential code paths as you write your code. Do not plan to handle “unusual” cases later: you’ll forget and your code will be buggy. Bug Hunting Programmers write code. Programmers aren’t perfect. The programmer’s code isn’t perfect. It therefore doesn’t work perfectly the first time. So we have bugs. We should always employ sound engineering techniques that minimize the likelihood of unpleasant surprises. Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. Reduce bugs to the simplest set of steps possible. reproduction Ensure that you are focusing on a single problem. Assertions and logging ( ) are potent debugging tools. Use them often. even the humble console.log and nodejs assert Binary chop problem spaces to get results faster. As you develop your software, invest time to write a suite of unit tests. Untested code is a breeding ground for bugs. Tests are your bleach. Learn how to use your debugger well. Then use it at the right times. Fix bugs as soon as you can. Don’t let them pile up until you’re stuck in a code cesspit. Debugging isn’t easy. But it’s our own fault. We wrote the bugs. Always test your code Unit tests specifically exercise the smallest “units” of functionality in isolation, to ensure that they each function correctly. This isolation specifically means that a unit test will not involve any external access: no database, network, or file system operations will be run. Quality is free, but only to those who are willing to pay heavily for it. To improve our software development we need rapid feedback, to learn of problems as soon as they appear. Good testing strategies provide short feedback loops. Write tests as you write the code under test. Do not postpone test writing, or your tests will not be as effective. All tests should run on your build server as part of a continuous integration tool chain. Test whatever is important in your application. Global variables and singleton objects are anathema to reliable testing. You can’t easily test a unit with hidden dependencies. Factoring your code to make it “testable” leads to better code design. Program testing can be used to show the presence of bugs, but never to show their absence. How to deal with complexity Simplicity is a great virtue but it requires hard work to achieve it and education to appreciate it. And to make matters worse: complexity sells better. Complexity is generally accidental, rarely something someone adds willfully. Defer design decisions until you have to take them. Don’t make architectural decisions when you don’t know the requirements yet. Don’t guess. Practice Makes Perfect A programmer needs good taste and a sense of aesthetics to write exceptional code. Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius — and a lot of courage — to move in the opposite direction. Good software development is not cowboy coding, throwing down the first code you can think of. It is a deliberate, considered, accurate endeavor. Good programmers work with humility. They admit that they don’t know it all. Good code and good coders are born from a desire to write the right thing in the right way. Be a team player Programming teams have a set of rules. These rules define what we do and how we do it. But they also describe a coding culture. Don’t rely on vague unwritten team “rules.” Make the implicit rules explicit, and take control of your coding culture. Apply bug fixes to the root cause, not where symptoms manifest. Sticking plaster symptom-fixes do not lead to simple code. Avoid implicit assumptions in your code. Only write as much code as is needed. Anything extra is complexity that will become a burden. Stop and think. Don’t write stupid code. Admit to your mistakes and bad coding decisions. Learn from them. Have the courage to use your brain. Feel empowered to critique code and make decisions about how to improve it. Learn what makes software easy to change, and strive to craft software with these attributes. To modify code you need courage and skill. Not recklessness. Often it is best to make a series of frequent, small, verifiable adjustments, rather than one large sweeping code change. Avoid copy-and-paste coding. Factor your logic into shared functions and common libraries, rather than suffer duplicated code (and duplicated bugs). Write small, modular sections of code. Keep it clean and neat. Code should be “shared” because it is useful to multiple clients, not because the developers want to create a nifty shared library. Don’t dismiss other people’s code. It may be better to use existing libraries rather than write your own version. Creating software releases requires discipline and planning. It is more than hitting “build” in a developer’s IDE. Always build your software in a fresh checkout, from scratch. Never reuse old parts of a software build. Make your build as simple as a single step that automates all parts of the process. Use a scripting language to do this. Deploy your builds on a CI server to ensure their health. Make formal releases from the same system. Be in a state of continual learning. Always look to learn something new. Our learning is often too narrowly focused. Consider a wider sphere of reference. Draw inspiration from many fields. Takes notes as you learn. Even if you throw them away. If you can’t explain it simply, you don’t understand it well enough. Teach a topic to learn that topic well. I hear and I forget. I see and I remember. I do and I understand. Using what you just learned cements it in your memory. Try examples, answer questions, create pet projects. Be wary of stagnation. Seeking to become a better programmer, by definition, is not the most comfortable lifestyle. Expect to invest time and effort to grow your skill set. This is a worthwhile investment; it will repay itself. Do not make yourself “indispensable” by writing unreadable or unnecessary “clever” code. Honour software licenses. Don’t become a one-trick pony. Position yourself to face new challenges, learn, and grow as a developer. Love All Languages Learn languages that follow different idioms and paradigms. Consider also learning some “dead” languages that are no longer commonly used, to understand the history of your craft. A good programmer knows many languages, and multiple idioms, broadening their palette of solutions. It improves the code they write. Working with your programming language is a relationship you have to work at each day. To write the best code in a language, you should commit to its styles and idioms rather than force your own upon it. Good programmers are good communicators. They talk, write, code, listen, and read well. Don’t expect to become a language master overnight, and don’t get frustrated whilst you work at it. Concentrate effort on the most important things first. What is most urgent, or will produce the most value? If you do something often, make the computer do it for you. Automate it with a script. Split large tasks up into a series of smaller, well-understood tasks. You will be able to judge progress through these more accurately. Make sure you define “done.” If you can’t tell when it’s done, then you shouldn’t start it. Use tests written in code to define when your code is complete and working. Don’t do more work than necessary. Work until you’re “done.” Then stop. When facing a problem, make sure you’ve considered more than one approach to solve it. Only then should you start working on it. Purposefully place yourself beside excellent programmers. More comments do not necessarily make your code better. Communicative code does not need extra commentary to prop it up. Learn about development methodologies, trends, manifestos, and fads. If you found this post helpful, please share it so that others can find it. You can follow me on GitHub and LinkedIn . If you have any ideas and improvements feel free to share them with me. 💪 Happy coding!

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