In my last 3 articles I convinced you to , , and . Now I’m going try to convince you to eliminate the switch statement. remove the if statement kill the for loop never use break While the switch statement is useful, it doesn’t quite fit in with the rest of our functional code. It’s not Immutable, it can’t be composed with other functions, and it’s a little side effecty. Switch also uses , which is also anti-functional. (Find out why is so horrible in the article below) break break _In my last article, Death of the for Loop, I tried to convince you to abandon the for loop for a more functional…_hackernoon.com Rethinking JavaScript: Replace break by going functional What I really want is something immutable and free of side effects. Something I can pass one value in and get one value out. You know, something functional! Let’s dig right in and take a look at an example straight from the . redux website function counter(state = 0, action) {switch (action.type) {case 'INCREMENT':return state + 1case 'DECREMENT':return state - 1default:return state}} I tried playing with this a bit and ended up converting it to a nested ternary. const counter = (state = 0, action) =>action.type === 'INCREMENT' ? state + 1: action.type === 'DECREMENT' ? state - 1: state (If you find this syntax confusing, then check out this article, it will explain 's and nested ternary.) if _Thinking functionally has opened my mind about programming._medium.com Rethinking JavaScript: The if statement This is better, but one thing I didn’t like was repetition of . So then I thought I could probably use an object literal. I could also create a function to wrap the object literal and at the same time add support for a default case. action.type === function switchcase (cases, defaultCase, key) {if (cases.hasOwnProperty(key)) {return cases[key]} else {return defaultCase}} Now let’s curry this bad boy, convert the to a ternary and ES6 it up a bit! if const switchcase = cases => defaultCase => key =>cases.hasOwnProperty(key) ? cases[key] : defaultCase Sexy! Now our reducer would look like this… const counter = (state = 0, action) =>switchcase({'INCREMENT': state + 1,'DECREMENT': state -1})(state)(action.type) The problem with this early version of is the entire object literal is evaluated before being passed to the function. This means and are both evaluated. This can be very dangerous… No bueno. switchcase switchcase state +1 state -1 Hmm… if the values in the object literal were functions, then they could be executed only when there is a matching case. So let’s create a companion function called (F is for function), which is just like except it’s values are functions. switchcaseF switchcase const switchcaseF = cases => defaultCase => key =>switchcase(cases)(defaultCase)(key) () Now the reducer’s values can be changed to functions and only the matching case will be evaluated. const counter = (state = 0, action) =>switchcaseF({'INCREMENT': state + 1,'DECREMENT': state -1})( state)(action.type) () => () => () => …but I kinda want these functions to be . So let’s try adding this… optional const executeIfFunction = f =>f instanceof Function ? f() : f const switchcaseF = cases => defaultCase => key =>executeIfFunction(switchcase(cases)(defaultCase)(key)) Now our redux reducer can look like this (notice the default value)… const counter = (state = 0, action) =>switchcaseF({'INCREMENT': () => state + 1,'DECREMENT': () => state -1}) (action.type) (state) OK, not vastly different, but we could do stuff like this. (added a RESET) const counter = (state = 0, action) =>switchcaseF({ 'INCREMENT': () => state + 1,'DECREMENT': () => state -1})(state)(action.type) 'RESET': 0, Another Example This example is taken from http://www.w3schools.com/js/js_switch.asp var day; switch (new Date().getDay()) {case 0:day = "Sunday";break;case 1:day = "Monday";break;case 2:day = "Tuesday";break;case 3:day = "Wednesday";break;case 4:day = "Thursday";break;case 5:day = "Friday";break;case 6:day = "Saturday";} Because we have properly curried like good boys and girls we can decompose this switch to multiple reusable methods, and we all know… switchcase making our code reusable should always be one of our goals. const getDay = switchcase({0: 'Sunday',1: 'Monday',2: 'Tuesday',3: 'Wednesday',4: 'Thursday',5: 'Friday',6: 'Saturday'})('Unknown') const getCurrentDay = () =>getDay(new Date().getDay()) const day = getCurrentDay() Here we have separated out all the logic from our impure function into a pure function. This will make testing and much easier. getCurrentDay getDay function composition _Function composition has got to be my favorite part of functional programming. I hope to provide you with a good real…_hackernoon.com Functional JavaScript: Function Composition For Every Day Use. Extra Credit Now we can do cool things like create a programatically! switchcase const days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'] const getDay = switchcase(days.reduce((acc, value) =>(acc[value] = `The day is ${value}.`, acc), {}))("I don't know what day it is.") console.log(getDay('Monday')) // 'The day is Monday. This isn’t the greatest example. There are obvious and better ways to generate this sentence, I’m just trying to demo what the can do, so cut me some slack! switchcase The Code Here’s our final, pure, immutable and functional code. switchcase 3rd Party Libraries For those interested in digging deeper into the functional world, there are some great libraries out there I would like to recommend. — Ramda is a functional library similar to lodash and underscore. Check out Ramda’s function. The functionality if similar to this and a great alternative! Ramda cond switchcase — lodash/fp is the functional version of lodash. It’s worth taking a look. lodash/fp — One of the more popular functional libraries for JavaScript. Fantasy Land Summary The switch statement doesn’t fit into our functional paradigm, but we can create a function that has similar characteristics. Doing so let’s us decompose the switch into smaller and reusable pieces. We can even generate one programatically! I know it’s a small thing, but it makes my day when I get those follow notifications on Medium and Twitter ( ). Or if you think I’m full of shit, tell me in the comments below. @joelnet Cheers! note: before you flip out about not supporting ‘fall-through’, this is because I didn’t have a need for it in my project. It’s not meant to be an exact replica of . or something. switchcase switch YAGNI Related Articles _JavaScript’s for loop has served us well, but it is now obsolete and should be retired in favor of newer functional…_hackernoon.com Rethinking JavaScript: Death of the For Loop _I love the new Promise library that ships with ES6, though one thing has been left out, a function to sequentially…_medium.com Functional JavaScript: Resolving Promises Sequentially
