2017-03-12-3-array-hacks.md

layout	title	tip-number	tip-username	tip-username-profile	tip-tldr	categories
post	3 Array Hacks	64	hassanhelfi	https://twitter.com/hassanhelfi	Arrays are everywhere and with the new spread operators introduced in ECMAScript 6, you can do awesome things with them. In this post I will show you 3 useful tricks you can use when programming.	en javascript

Arrays are everywhere in JavaScript and with the new spread operators introduced in ECMAScript 6, you can do awesome things with them. In this post I will show you 3 useful tricks you can use when programming.

1. Iterating through an empty array

JavaScript arrays are sparse in nature in that there are a lot of holes in them. Try creating an array using the Array’s constructor and you will see what I mean.

> const arr = new Array(4);
[undefined, undefined, undefined, undefined]

You may find that iterating over a sparse array to apply a certain transformation is hard.

> const arr = new Array(4);
> arr.map((elem, index) => index);
[undefined, undefined, undefined, undefined]

To solve this, you can use Array.apply when creating the array.

> const arr = Array.apply(null, new Array(4));
> arr.map((elem, index) => index);
[0, 1, 2, 3]

2. Passing an empty parameter to a method

If you want to call a method and ignore one of its parameters, then JavaScript will complain if you keep it empty.

> method('parameter1', , 'parameter3');
Uncaught SyntaxError: Unexpected token ,

A workaround that people usually resort to is to pass either null or undefined.

> method('parameter1', null, 'parameter3') // or
> method('parameter1', undefined, 'parameter3');

I personally don’t like using null since JavaScript treats it as an object and that’s just weird. With the introduction of spread operators in ES6, there is a neater way of passing empty parameters to a method. As previously mentioned, arrays are sparse in nature and so passing empty values to it is totally okay. We'll use this to our advantage.

> method(...['parameter1', , 'parameter3']); // works!

3. Unique array values

I always wonder why the Array constructor does not have a designated method to facilitate the use of unique array values. Spread operators are here for the rescue. Use spread operators with the Set constructor to generate unique array values.

> const arr = [...new Set([1, 2, 3, 3])];
[1, 2, 3]