17 Pro JavaScript tricks you didn't know

There are many ways to write code but generally the first way for many people is very long and can take you some time. Here is my latest post that will increase your efficiency and productivity when coding JavaScript.

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JavaScript : Tricks You Should Know

The ternary operator

Noobs:

let hungry = true;
let eat; 
if (hungry == true) {
       eat = 'yes'; 
} else {
       eat = 'no';
}

Pro:

let hungry = true;
let eat = hungry == true ? 'yes' : 'no';

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Number to string / string to number

Noobs:

let num = 15; 
let s = num.toString(); // number to string
let n = Number(s); // string to number

Pro:

let num = 15;
let s = num + ""; // number to string
let n = +s; // string to number

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Populating an array

Noobs:

for(let i=0; i < arraySize; i++){
       filledArray[i] {'hello' : 'goodbye'};
}

Pro:

let filledArray = new Array(arraysize).fill(null).map(()=> ({'hello' : 'goodbye'}));

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Dynamic properties in objects

Noobs:

let dynamic = "value"; 
let user = {
     id: 1,
};
user[dynamic] = "other value"; 

Pro:

let dynamic = "value"; 
let user = {
    id: 1,
    [dynamic] = "other value"
};

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Read more => 3 Steps to learn a programming language

Removing duplicates

Noob:

let array = [100, 23, 23, 23, 23, 67, 45]; 
let outputArray = [];
let flag = false; 
for (j = 0; < array.length; j++) {
   for (k = 0; k < outputArray.length; k++) {
      if (array[j] == outputArray[k]) {
         flag = true;
       }
    }
    if (flag == false) {
      outputArray.push(array[j]);
     }
     flag = false;
}
//outputArray = [100, 23, 67, 45]

Pro:

let array = [100, 23, 23, 23, 23, 67, 45]; 
let outputArray = Array.from(new Set(array)); 
//outputArray = [100, 23, 67, 45]

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Array to object

Noob:

let arr = ["value1", "value2", "value3"]; 
let arrObject = {};
for (let i = 0; i < arr.length; ++i) {
   if (arr[i] !== undefined) {
     arrObject[i] = arr[i];
   }
}

Pro:

let arr = ["value1", "value2", "value3"]; 
let arrObject = {...arr}; 

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Read more => A guide to Geolocation API

Object to Array

Noob:

let number = {
  one: 1, 
  two: 2,
};
let keys = []; 
for (let numbers in numbers) {
  if (number.hasOwnProperty(number)) {
     keys.push(number);
    }
}
// key = [ 'one', 'two' ]

Pro:

let number = {
  one: 1, 
  two: 2,
};
let key = Object.keys(numbers); // key = [ 'one', 'two' ]
let value = Object.values(numbers);  // value = [ 1, 2 ]
let entry = Object.entries(numbers); // entry = [['one' : 1], ['two' : 2]]

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Short circuit conditionals

Noob:

if (docs) {
    goToDocs();
}

Pro:

docs && goToDocs()

---

Read more => "use strict" in JavaScript

Use ^ to check if numbers are not equal

if(a!=123) // before // NOOBS

if(a^123) // after // PRO

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Loop over an object

const age = {
   Rahul: 20,  
   max: 16
};

// Solution 1 - Get 'keys' and loop over
const keys = Object.keys(age); 
keys.forEach(key => age[key]++);

console.log(age); // { Rahul: 21, max: 16 }

// Solution 2 - for ..in loop
for(let key in age){
   age[key]++;
}

console.log(age); // { Rahul: 22, max: 18 }

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Object keys are stored in insertion order

cosnt obj = {
  name: "Rahul", 
  age: 16, 
  address: "Earth", 
  profession: "Developer", 
}; 

console.log(Object.keys(obj)); // name, age, address, profession

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Check if value is an array

const arr = [1, 2, 3]; 
console.log(typeof arr); // object
console.log(Array.isArray(arr)); // true

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Initialize an array of size n and fill with default values

const size = 5;
const defaultValue = 0;
const arr = Array(size).fill(defaultValue);
console.log(arr); // [0, 0, 0, 0, 0]

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Truthy and False values

False values => false, 0, ""(empty string), null, undefined, &NaN.

Truthy values => "Values", "0", {}(empty object), &[](empty array)

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Difference between double equal and triple equal

// Double equal - Converts both the operands to the same type and then comapares
console.log(0 == 'o'); // true

// Triple Equal - Does not convert t same type
console.log(0 === '0'); // false

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Better way to accept arguments

function downloadData(url, resourceId, searchTest, pageNo, limit) {}

downloadData(...); // need to remember the order

Simpler way to do:

function downloadData(
{ url, resourceId, searchTest, pageNo, limit } = {}
) {}

downloadData(
  { resourceId: 2, url: "/posts", searchText: "WebDev" }
);

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null vs undefined

null => It is a value whereas undefined is not.

null is like an empty box and undefined it not box at all.

const fn = (x = 'default value') => console.log(x);

fn(undefined); // default value
fn(); // default value

fn(null); // null

When null is passed, the default value is not taken. Whereas, when undefined or nothing is passed the default value is taken.

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⚡Thanks For Reading | Happy Coding 🍺

Comments

[Michael Z]

// Noobs:

let num = 15; 
let s = num.toString(); // number to string
let n = Number(s); // string to number

// Pro:

let num = 15;
let s = num + ""; // number to string
let n = +s; // string to number

Sorry, but clever != pro. The "Noob" version much better reveals the intent of the code.

[Aral Roca]

Same for

if(a!=123) // before // NOOBS

if(a^123) // after // PRO

a^123 is not very clean IMO. Maybe a better one will be if(a !== 123)

[Aral Roca]

And it's not correct for decimal numbers.

Boolean(122^123) // true
Boolean(123.1^123) // false -> is not correct, should be true 123.1 !== 123
Boolean(123^123) // false

Much better to use the !== operator.

[Miguel Ruiz]

Also we should think this is something that someone who comes from another Programming Language won't understand easily, just for saving 1 character

[Joan León]

IMHO

if(a!=123) // before // NOOBS

if(a!==123) // after // PRO

[Luis Vegerano]

I would never approve a PR with something like that.

[Rahul]

I agree. But you know the pro version is better when you know many things about JS and doing big projects. I too had some doubt when writing this.

[Mišo]

Sorry, but I have to strongly disagree. Please don't make people think it's better to complicate things. The Noob version is actually a Pro especially in big projects. I already wrote it here dev.to/misobelica/comment/15b21

JS is not the best language even without these quirks. We should know them but consider them a very sad code smell and not a Pro version.

[Rahul]

I'm sorry sir. When i will post again something related to this i will surely keep this in mind. Currently i'm writing through my phone so it will be hard for me to do. I'm sorry once again

[Hans Spaans]

I wouldn't say better as it reduces the readability and maintainability of the code a lot. Having a language with strict type casting may seem a hassle for some, but it saves you hours of debugging in the long run. It was one of the significant reasons for the development of TypeScript and as a goal for both PHP 7 and Python 4.

[Rahul]

People write codes with their read comfort ability.

[Seanmclem]

Pretty much the #1 rule when learning programming is to not only write for yourself but with future coders and teammates in mind.

[Zhitomir Oreshenski]

It is not readable and maintainable in the long run.

[Rahul]

Agree.

[Madza]

was going to say that too 😉

[Asaju Enitan]

I am not so cool with the "pro" code, def not advisable for team based projects

[spO0q]

Before anything, thanks for sharing. These are funky tips, and it's always interesting to read posts like yours.

However, I prefer not being "clever", especially in a pro context. I want everybody to understand what I'm doing rather than being regarded as a code ninja. To me, if it's harder to read, it's worse, not better.

Maybe the "pros vs. noobs" presentation is not the best here. Likewise, I can assure you that big projects require clarity. If it's too "clever", it's harder to maintain.

[Rahul]

I surely agree with this and i will keep this in mind. I'm sorry actually I'm using my phone for blogging. I'm sorry.

[spO0q]

No problem, thanks for sharing :)

[bugb]

Your code is incorrect

let dynamic = "value"; 
let user = {
    id: 1
    [dynamic] = "other value"
};

It should be

let dynamic = "value"; 
let user = {
    id: 1,
    [dynamic]: "other value"
};

[Rahul]

That comma though. I'm sorry

[Adam Azad]

So is =. It should be a colon :

let dynamic = "value"; 
let user = {
    id: 1,
    [dynamic]: "other value"
};

[Ivan Pozderac]

Have you ever worked in a team where you have senior, mid, 2+ juniors and intern?

senior and mid are like fish in the water with 'pro' code while juniors and interns feel like fish on a tree!

Clever code is ok to have on small teams where level of knowledge is similar. Having clever code in a larger teams leads to codebase nightmares.

Code should always be readable and easy to understand for everyone who will work on it. If you have to explain it, then your code is just a bad joke!

[Andrej Rypo]

if(a!=123) // legible to anyone
if(a^123) // wtf

I don't believe this code actually improves anything, like many other snippets presented here. It sacrifices one keyboard hit for legibility.

While I might be dumb for not knowing the trick, the difficulty is to make the code better understandable, not vice versa.

[Aral Roca]

And doesn't work as expected.... Boolean(123.1^123) // false, but should be true

[Brian Hogg]

Yeah, the XOR operator isn't doing an equivalence check, at least not in the way the OP is presenting. It's just not a relevant tool to use, I don't think.

[Alice Fernandes]

let num = 15;
let s = num + ""; // number to string
let n = +s; // string to number

I don't believe that this is pro javascript. This is playing with types of js and praying that it doesn't break in the future. I believe that converting to other types should be explicit so that it becomes readable to other coders

[Rahul]

Yea agree.

[Ivan Pozderac]

When I think about it, I have to say that I completely agree with you.

While I'm comfortable to read 'PRO' code, I find myself writing readable code even in personal projects and stuff I'm just trying out that will never be seen by anyone else.

I guess it is a force of habit.

Clever code led us to having 'rockstar ninja developers' - writing 'PRO' code just to look clever and to confuse others to gain leverage and opportunity to explain something that shouldn't need explanation in the fist place.

You are 100% correct on this one!

[Rahul]

I can see someone understanding me. Sigh of happiness finally

[Jakub T. Jankiewicz]

Please check your code by running it first:

This is syntax error, because it's not valid JavaScript:

for(let i=0; i < arraySize; i++){
       filledArray[i] {'hello' : 'goodbye'};
}

missing =, another is this, that suppose to be true but the character is not zero is letter o and even lowercase.

console.log(0 == 'o')

[Peter Ellis]

The trouble with some of these is that while they may save a negligible amount of writing time, they certainly do increase reading time. Reason being, nobody reads character by character, it's closer to token by token.

A good example is your Removing duplicates snippet: you're replacing over 20 tokens (some of them loops and ifs, which are even more taxing to parse), with 5 simple ones. Brilliant! Best of all, it doesn't matter how skilled you are, the "pro" option is easier to read for everyone. And this is key.

Because if we look at the convert string/number and back snippet. num.toString() is two simple and verbose tokens in a not-at-all surprising sequence. You don't even have to know that num is a number to understand what's going on. Great! How about "" + num? Well, in terms of tokens it isn't any shorter. However it also includes a non-intuitive use of +. As you're not using the main effect of + (i.e. adding/concatenating) two things but a secondary effect (type coercion).

Same goes for the reverse direction, except there you also add another confounding construct: = +. Which will definitely have most people stop for a moment to re-parse it, because we very rarely put two separate operators after each other.

Some people say "ah, but once you get used to them, it becomes second nature and you can read it as fast as the noob versions". That is true, but note how it isn't actually faster: what you've achieved is that you spent a lot of time learning to read structures "noobs" can't read.

And that's my biggest criticism of lists like these. I don't think it was your intention but the noob/pro distinction creates a gate-keeping effect, where certain coding practices are followed not for any tangible improvement in code quality but to signal belonging to a group, in other words, they're a shibboleth.

[Thr0TT1e]

ERROR - "Object to Array"

// Noobs:

let number = {
    one: 1,
    two: 2,
};
let keys = [];
for (let numbers in number) {
    if (number.hasOwnProperty(numbers)) {
        keys.push(numbers);
    }
}

console.log(keys) // [ 'one', 'two' ]

// Pro:

let number = {
    one: 1,
    two: 2,
};
let key   = Object.keys(number) // [ 'one', 'two' ]
let value = Object.values(number) // [ 1, 2 ]
let entry = Object.entries(number) // [ [ 'one', 1 ], [ 'two', 2 ] ]

[Rahul]

Everyone has their own perspective sir.

[Meg Stepp]

No he meant your had typos in your variable names. You declared a "number" variable but referenced "numbers" (with an s) in your code examples. The code literally doesn't run.

[Rahul]

Agreed.