Array Destructuring

By  on  

Destructuring has become a major language feature in JavaScript, most prominently seen with imports, but also in function declarations and so on.  While object literals are the usual case for destructuring, remember that you can also destructure Arrays and Sets. Let's have a look at how destructuring is used for arrays and Sets!

The usual case for destructuring is with an object literal:

const dict = { prop1: "one", prop2: "two" };

const { prop1, prop2 } = dict;
// prop1 = "one"
// prop2 = "two"

The syntax for Array and Set destructuring is a bit different:

const arr = ["uno", "dos"];

const [one, two] = arr;
// one = "uno"
// two = "dos"

// Or more explicitly
const [width, height] = [200, 400];

The destructuring syntax within iteration looks like:

const items = [
    ["one", "two"],
    ["three", "four"]
];
items.forEach(([uno, dos]) => {
    console.log(uno, dos);
});

// "one", "two"
// "three", "foor"

You can also clone an array with destructuring:

const arr = ["one", "two"];
const clone = [...arr];

You can also use commas to your advantage if you don't care about a given index of an array:

const arr = [1, 2, 3, 4];

const [,,,four] = arr; // four === 4

Destructuring is awesome for skilled JavaScript developers and can be confusing to newcomers.  Basic array destructuring doesn't mislead too much but iterating can be an ugly snippet.  Taking a minute to see these reduced examples may help you too better understand the pattern.

Recent Features

  • By
    Responsive Images: The Ultimate Guide

    Chances are that any Web designers using our Ghostlab browser testing app, which allows seamless testing across all devices simultaneously, will have worked with responsive design in some shape or form. And as today's websites and devices become ever more varied, a plethora of responsive images...

  • By
    How I Stopped WordPress Comment Spam

    I love almost every part of being a tech blogger:  learning, preaching, bantering, researching.  The one part about blogging that I absolutely loathe:  dealing with SPAM comments.  For the past two years, my blog has registered 8,000+ SPAM comments per day.  PER DAY.  Bloating my database...

Incredible Demos

  • By
    Create a Sexy Persistent Header with Opacity Using MooTools or jQuery

    I've been working with the Magento eCommerce solution a lot lately and I've taken a liking to a technique they use with the top bar within their administrative control panel. When the user scrolls below a specified threshold, the top bar becomes attached to the...

  • By
    JavaScript Canvas Image Conversion

    At last week's Mozilla WebDev Offsite, we all spent half of the last day hacking on our future Mozilla Marketplace app. One mobile app that recently got a lot of attention was Instagram, which sold to Facebook for the bat shit crazy price of one...

Discussion

  1. Charles Robertson

    Hi David. This is really great, but what is the point of destructuring? Is it just a more concise way of writing objects?

  2. Other nice use cases to mention:

    Iterating over objects

    const myObject = { /* ... */ }
    
    for (const [ key, value ] of Object.entries(myObject)) {
      // ...
    }
    

    Omitting unneeded values by just using some commas:

    const [,, month] = '2018-07-31'.match(/^[0-9]{4}.([0-9]{2}).[0-9]{2}$/)
    

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!