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7 Useful JavaScript Tricks

By David Walsh on April 16, 2019

Just like every other programming language, JavaScript has dozens of tricks to accomplish both easy and difficult tasks. Some tricks are widely known while others are enough to blow your mind. Let's have a look at seven JavaScript tricks you can start using today!

Get Unique Values of an Array

Getting an array of unique values is probably easier than you think:

var j = [...new Set([1, 2, 3, 3])]
>> [1, 2, 3]

I love the mixture of rest expression and Set!

Array and Boolean

Ever need to filter falsy values (0, undefined, null, false, etc.) out of an array? You may not have known this trick:

myArray
    .map(item => {
        // ...
    })
    // Get rid of bad values
    .filter(Boolean);

Just pass Boolean and all those falsy value go away!

Create Empty Objects

Sure you can create an object that seems empty with {}, but that object still has a __proto__ and the usual hasOwnProperty and other object methods. There is a way, however, to create a pure "dictionary" object:

let dict = Object.create(null);

// dict.__proto__ === "undefined"
// No object properties exist until you add them

There are absolutely no keys or methods on that object that you don't put there!

Merge Objects

The need to merge multiple objects in JavaScript has been around forever, especially as we started creating classes and widgets with options:

const person = { name: 'David Walsh', gender: 'Male' };
const tools = { computer: 'Mac', editor: 'Atom' };
const attributes = { handsomeness: 'Extreme', hair: 'Brown', eyes: 'Blue' };

const summary = {...person, ...tools, ...attributes};
/*
Object {
  "computer": "Mac",
  "editor": "Atom",
  "eyes": "Blue",
  "gender": "Male",
  "hair": "Brown",
  "handsomeness": "Extreme",
  "name": "David Walsh",
}
*/

Those three dots made the task so much easier!

Require Function Parameters

Being able to set default values for function arguments was an awesome addition to JavaScript, but check out this trick for requiring values be passed for a given argument:

const isRequired = () => { throw new Error('param is required'); };

const hello = (name = isRequired()) => { console.log(`hello ${name}`) };

// This will throw an error because no name is provided
hello();

// This will also throw an error
hello(undefined);

// These are good!
hello(null);
hello('David');

That's some next level validation and JavaScript usage!

Destructuring Aliases

Destructuring is a very welcomed addition to JavaScript but sometimes we'd prefer to refer to those properties by another name, so we can take advantage of aliases:

const obj = { x: 1 };

// Grabs obj.x as { x }
const { x } = obj;

// Grabs obj.x as { otherName }
const { x: otherName } = obj;

Useful for avoiding naming conflicts with existing variables!

Get Query String Parameters

For years we wrote gross regular expressions to get query string values but those days are gone -- enter the amazing URLSearchParams API:

// Assuming "?post=1234&action=edit"

var urlParams = new URLSearchParams(window.location.search);

console.log(urlParams.has('post')); // true
console.log(urlParams.get('action')); // "edit"
console.log(urlParams.getAll('action')); // ["edit"]
console.log(urlParams.toString()); // "?post=1234&action=edit"
console.log(urlParams.append('active', '1')); // "?post=1234&action=edit&active=1"

Much easier than we used to fight with!

JavaScript has changed so much over the years but my favorite part of JavaScript these days is the velocity in language improvements we're seeing. Despite the changing dynamic of JavaScript, we still need to employ a few decent tricks; keep these tricks in your toolbox for when you need them!

What are your favorite JavaScript tricks?

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Discussion

Marie Thomas
Thanks for sharing these JavaScript tricks. All tricks are awesome but Merge Objects is my favorite one as it helps to make your task much easier and speed up my work. Keep up the great work.
Yan Bloch
Regarding “filter falsy values”, you could use reduce function for single iteration.
Brian De Sousa
Great list! I must be living under a rock because I hadn’t heard of URLSearchParams yet. That’s awesome!

David Hibshman

Convert arrays element types:

// number to strings
var strArr = [1,2,3,4,5].map(String);
// ["1","2","3","4","5"]

Joel Brighton
Nice! I also particularly like the URLSearchParams tip.

My only (friendly) word of caution in using ‘tricks’ (not necessarily those above) is that obscure coding practices can sometimes cause more confusion than they’re worth. (Of course, what’s obscure can be a matter of perspective). :)
Maximilian Berkmann
And the good ol:
exp | 0 instead of Math.floor(exp) and the exp | 1/Math.ceil(exp) equivalent.

And the ones using bit shifts.

Michal Zalecki
These aren’t true equivalents
```
0 | 1               // 1
Math.ceil(0) // 0
```

Anh Tran
URLSearchParams is amazing. It’s been a while struggling with query string and all the regex stuff!
James
Should isRequired throw a ReferenceError instead?
Jakub Słowik
Is it just me or the Math.floor() and Math.ceil() is better in comparison to exp | 0 and exp | 1. It’s just more readable.

Ujjwal Singha Roy
for Math.floor() you can use short circuit operator
~~

Example: Math.floor(2.3) is equivalent and faster with ~~(2.3)

Avraham Hamu
what is the impact if we create an empty object with {}? why does __proto__ is an issue? is it a performance issue?

Rubén S. García
Maybe not too much, but if you consider that the Object will be used for the solely purpose of being a dictionary, like a Map, it makes sense to “cleanup” the Object :). I’m not a JS expert nor performance wizard either so I may be wrong too.

Tobi Reif
Shortcuts for updating a variable based on its current value:
```
let speed = 10;
speed *= 2;
// → 20
speed += 10;
// → 30
```
Jordan Ball
In your tip on filtering falsey values, I don’t understand why you included the map() method in your illustration. From a pedagogical perspective, it does nothing except cause a reader’s attention to focus on a non-issue.

Rich

Favorite ES trick- Quick value “flip-flopping” between two variables without an intermediary variable: (change a to b, change b to a)

Could be done before but was super funky:

let a = 'thing';
let b = 'otherThing';

/* Works because of destructuring */
 [a,b]=[b,a]; // a is now 'otherthing', b is now 'thing'

/* (Old Super-Funky Way) */
  b = [a, a=b][0]; // Works, but barely understandable

Rubén S. García
The swap function trick is cool, plus, IMHO, it’s very easy to understand what’s going on if you rely, as myself, heavily on destructuring syntax in JS.

K L Estes
Not a javascript trick per se, but still interesting:
```
x = x ^ y
y = x ^ y
x = x ^ y
```
…and swapped !

Rubén S. García
I remember this trick from assembly language.

Mossa
to get red of falsy values you can just type
```
array.filter(e=>e)
```
Andriy Haydash
Thanks for the great tips.

The first one with Set and transforming it back into an array is a neat one.
Rubén S. García
Very interesting tricks here :). I learned the other day that using the ?. optional chaining operator you can, besides accessing properties, call functions!
```
const adventurer = {
  name: 'Alice',
  cat: {
    name: 'Dinah'
  }
};

const dogName = adventurer.dog?.name;
console.log(dogName);
// expected output: undefined

console.log(adventurer.someNonExistentMethod?.());
// expected output: undefined
```
verbatim from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining

MDN is great!