Here’s a few and traps that beginners should probably know of. If you’re already an expert, feel free to read this with a knowing look. tricks javascript Javascript is just another programming language. What could possibly go wrong ? 1. Did you ever try to sort an array of numbers ? Javascript uses alphanumeric sort per default. sort() So will output [1,2,5,10].sort() [1, 10, 2, 5]. To properly sort an array, you can use [1,2,5,10].sort((a, b) => a — b) Easy solution, provided you knew there was a problem in the first place :) 2. new Date() is just wonderful can accept: new Date() no argument: returns now one argument : returns 1st of january 1970, + x milliseconds. Unix people know why. x new Date(1, 1, 1) returns 1901, february , 1. Because you know, the first one means 1 year after 1900, the second one is the month of the year (hence february) — who in his right mind would start indexing a table at indice 1 — , and the third one obviously is the day of the month, so 1 — because sometimes the indices do start at 1 — . second first Oh, and also new Date(2016, 1, 1) will not add 2016 years to 1900. It will simply represent the year 2016. 3. Replace does not replace I find it to be a good thing, as I don’t like functions that mutate their input. You also should know that will only replace the first match: replace If you wish to replace all occurences, you can use a regex with : /g "bob".replace(/b/g, 'l') === 'lol' // replace all occurences 4. Careful with comparisons Reason: [1,2,3] and [1,2,3] are two separate arrays. They just happen to contain the same values. They have distinct references and cannot be compared with === 5. Array is no primitive type To know if your var is an array, you can still use Array.isArray(myVar) 6. Closures This one makes a well known javascript interview question: Did you expect it to output 0, 1, 2… ? Do you know why it does not ? How would you fix it ? Let’s mention two of the possible solutions to this problem: Use instead of . Boom. solved. let var “The difference [between let and var] is scoping. is scoped to the nearest function block and is scoped to the nearest block (both are global if outside any block), which can be smaller than a function block.” ( e) var let enclosing sourc Alternative: use bind: Greeters.push(console.log.bind(null, i)) There are plenty of other ways to do this. These are only my top-2 choices :) 7. Speaking about bind What do you think this will output ? One point for you if you think this will crash with Cannot read property 'name' of undefined Reason: is not run with proper context. Again, there are many ways to solve this. greet I personally like This way you ensure that is called with your class instance as context. greet If you feel like should never be run out of context, you can also bind it in your class constructor: greet You should also know that fat arrows ( ) can be used to preserve the context. This will also work: => although I find this last example less elegant in our case. I’m glad we fixed this Conclusion Congrats, you’re now able to put stuff on the internet. Probably. Perhaps even without breaking everything (generally it does, though). Cheers \o/ Let me know if there’s anything I should have mentioned!

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Who said javascript was easy ?

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Companies Mentioned

Aurélien Hervé

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