Array.prototype.at

By  on  

Working with arrays is an essential skill in any programming language, especially JavaScript, as we continue to rely on external data APIs. JavaScript has added methods like find and `findIndex recently, but one syntax I love from languages like Python is retrieving values by negative indexes.

When you want to get the value of the last item in an array, you end up with an archaic expression:

const arr = ["zero", "one", "two", "three"];
const last = arr[arr.length - 1];

You could use pop but that modifies the array. Instead you can use at and an index, even a negative index, to retrieve values:

const arr = ["zero", "one", "two", "three"];
arr.at(-1); // "three"
arr.at(-2); // "two"
arr.at(0); // "zero"

at is a very little known function but useful, if only for the shorthand syntax!

Recent Features

  • By
    Page Visibility API

    One event that's always been lacking within the document is a signal for when the user is looking at a given tab, or another tab. When does the user switch off our site to look at something else? When do they come back?

  • By
    CSS @supports

    Feature detection via JavaScript is a client side best practice and for all the right reasons, but unfortunately that same functionality hasn't been available within CSS.  What we end up doing is repeating the same properties multiple times with each browser prefix.  Yuck.  Another thing we...

Incredible Demos

  • By
    Skype-Style Buttons Using MooTools

    A few weeks back, jQuery expert Janko Jovanovic dropped a sweet tutorial showing you how to create a Skype-like button using jQuery. I was impressed by Janko's article so I decided to port the effect to MooTools. The XHTML This is the exact code provided by...

  • 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

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