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5 neat JavaScript tips

Dalibor Belic on March 21, 2021

In this post, I'll show you 5 neat JavaScript tips that will help you become a better developer. Although this post requires some knowledge of Java...

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Kazppa • Mar 21 '21

May i ask some explanation about the "benefits" of destructuring ?

Akash Kava • Mar 22 '21

Destructuring improves speed by accessing members by one time assignment. Every a.b member expression is slower as it travels prototype chain for access.

The argument becomes immutable, reassigning destructred variable will not modify the source.

Kaleb M • Mar 22 '21

I don't think this would be true if the destructured key was an object, it would still be by reference.

Overall I agree that destructuring is cleaner though!

Akash Kava • Mar 24 '21

const user = { name: "Akash" };
let { name } = user;
name = undefined;
console.log(user.name);

Should it print undefined or "Akash"?

In no way destructured variable is by reference. Reassigning destructured variable is immutable (not changing property of object held in destructured variable if it is an object).

Kaleb M • Mar 24 '21

Yes, you assigned the string, so no not by reference. If name itself was an object, it would be by reference yea?

Akash Kava • Mar 24 '21

Try it and show me a working example.

Mihail Malo • Mar 24 '21

const user = { name: { first: "Akash", second: "Kava" } }
const { name } = user
name.first = "🅱️epis"
console.table(user.name)

Sir, please, there is no need to be rude.
(and yes, you will say to do const { name: { first } } = user, but pls. Pls. Sir, pls.)

Akash Kava • Mar 25 '21

In which way the word "Reassigning destructured variable" is similar to name.first = ... ? The whole purpose of destructuring is not to use member expression name.first. And yes let { name: { first } } = user is the correct way to use desctructering. user is immutable here. It is important to note that we can pass an object to a function which will not change the original object if function is written correctly using destructering. JavaScript compiler can also optimize it by knowing that the function is pure.

Vivek B • Mar 25 '21

Destructuring in itself doesn't make it immutable. In the example @akashkava where you re-assigned value to "name" variable and it didn't affect the original object is because the variable of type String (or any other primitives) are immutable and not because it is coming from a destructured object.
Your example is same as

let name = user.name; // string

which makes it immutable because of the data type. @qm3ster 's example showed that destructured values could be mutated which will mutate the origin object.

Destructuring is just syntactic sugar to provide more readability.
const name = user.name is same as const { name } = user

Dalibor Belic • Mar 21 '21

Sure.
I remember once a senior dev told me (I was a junior) that it's not just enough to do something. You have to do it the right way. Destructuring makes our code cleaner and more readable.

matgott • Mar 22 '21

Destructuring isn't working "with reference". This could be confusing.

Objects in Javascript are mutables, so if you are destructuring an object which one of it properties is another object, the variable created for that property will point to the same object in the Heap.

Blake Campbell • Mar 21 '21

I had no idea you could style console.logs, that's amazing!

Dalibor Belic • Mar 21 '21

Yep, pretty neat! :)

Riaan Pietersen • Mar 30 '21

In the days of ActionScript we were able to use a "with" statement.. kirupa.com/developer/actionscript/...

Is there something similar in JS?! I wonder.. :)

pris stratton • Mar 21 '21

The callback into Promise one is so handy. It means you can use async await as well which is so much easier to write.

Mafee7 • Mar 22 '21

Thx For the tip!

Dalibor Belic • Mar 22 '21

Welcome!

CodenameCookie • Mar 21 '21

There is a typo. You wrote 'trase' instead of 'trace'. Good article though.

Dalibor Belic • Mar 22 '21

Tnx!

Jon Portella • Mar 24 '21

FYI there's a Node.js util that does the promisifying for you, you don't need to write your own. Thanks for sharing!

Mihail Malo • Mar 25 '21

And a lot of nodejs builtins come in proper promise versions now, not by making you promisify them in userspace!

require("fs/promises").readdir('.').then(console.log)

Hurrah!

Benjamin Van Ryseghem • Mar 25 '21

obj.key is undefined, isn't it ?

Ali Taha Shakir • Mar 22 '21

What if I have 15-20 elements which I need to show in component, is it good / good practice to destructure 20 elements as arguments?

Dalibor Belic • Mar 22 '21

Yes! In that case, I would do the 2nd version: function (tiger) { ... and then inside the function: { endangered, latin, ... } = tiger