I learned Javascript the hard way: I stumbled into web development and kept on stumbling my way through the stack until I could program competently...
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one could even change this:
arr2 = arr1.map(function(a){return a.replace(/a/gi,"b")});to ES6 syntax:
arr2 = arr1.map(a => a.replace(/a/gi,"b"))Somewhat related -- if you're lazy like me, you might use map() simply to act on each item in the array (ignoring the fact that map creates a returns a new array). Don't do that! Use forEach() 👍
Just an addition to your article that I missed. One of the most important .map properties is that it returns a new array, it doesn't mutate current array. This is particularly useful in React/Redux, or where you want your objects to safely persist state.
I always find explicit for (or at least foreach) much are readable than all the different syntaxes of map appearing in different languages. Often It's better to explicitly write line or two more than to use fancy shorthands, especially if the codebase might get visited by juniors
its more apis to learn (map, find, some, every, filter, reduce) than just for-loop, but one you have done that and know where and why which function to use, value is huge.
Code speaks to you and just by reading one word you know intent what is supposed to happen. for-loop lacks such expressiveness, one have to dig into for-loop's body to understand why loop exists, what is doing.
And immutability on its own makes code so much easier to understand.
Fact that juniors also works on a project shouldn't sacrifice projects quality
On the contrary, juniors should get to know the FP side of languages like JavaScript as soon as possible. And the concepts behind it, like purity and immutability.
Really important:
Array.[map | find | some | every | filter | reduce]()key functions to handling arrays in easy, readable ways. It saves you a lot of hassle and a lot of ugly loops!Another addition is that methods like
map(and alsoforEach,every...) do not iterate over empty items. For example:new Array(5).forEach(console.log)doesn't print anything, so beware!Note: it doesn't mean they don't iterate over
undefinedvalues. Just empty, pristine slots that hasn't been assigned a value yet.So if you're thinking you could use
new Array(n).forEach(fn)to executefnntimes, you're out of luck. Also, that would generate a throwaway array, so it's sub-optimal. Useforfor that.(There's also this trick:
Array.from({ length: 3 }).forEach(console.log). It works, but it's kind of jarring. Again, I don't recommend doing that.)Others already pointed out that
mapreturns a new array. Good for immutability!Just so I'm clear as a junior:
map()does not mutate an array just makes a new one?Correct, array.map returns a new array that will not mutate your old one.
You could conceivably alter your original array while in the function executing on a key, but then you're out of the realm of using
I was about to ask if you meant a key as in an index in the array. I forgot that Arrays are objects in JavaScript, as pretty much everything else. But still, I am not sure what you mean by the function executing on a key.