JavaScript Array Group

By  on  

Managing, sorting, and manipulating data with JavaScript is a skill we've often delegated to third party libraries like lodash. As the JavaScript language progresses, however, these features eventually get. added to the JavaScript specification. Two such APIs for grouping of Array data are `Array.prototype.group and Array.prototype.groupToMap.

Array.prototype.group

To group an array of objects by a given property, call the group method with function that returns the grouping string:

const teams = [
  { name: "Arsenal", origin: "London", tier: "legendary" },
  { name: "Manchester United", origin: "Manchester", tier: "legendary" },
  { name: "Liverpool", origin: "Liverpool", tier: "legendary" },
  { name: "Newcastle United", origin: "Newcastle", tier: "mid" },
  // Lol, awful club
  { name: "Tottenham", origin: "London", tier: "lol" },
];

const tieredTeams = teams.group(({ tier }) => tier);

The result of the array's group is an object with keys that match the grouping key:

{
  legendary: [
    {name: "Arsenal", origin: "London", tier: "legendary"},
    {name: "Manchester United", origin: "Manchester", tier: "legendary"},
    {name: "Liverpool", origin: "Liverpool", tier: "legendary"}
  ], 
  mid: [
    {name: "Newcastle United", origin: "Newcastle", tier: "mid"}
  ], 
  lol: [
    {name: "Tottenham", origin: "London", tier: "lol"}
  ]
}

Array.prototype.groupToMap

groupToMap returns a Map instance instead of an object literal:

const tieredTeamsMap = teams.group(({ tier }) => tier);

tieredTeamsMap.has('lol') // true

tieredTeamsMap.get('lol') // [{name: "Tottenham", origin: "London", tier: "lol"}]

As of the time of publish, group and groupToMap are only available in Safari. These two methods are crucial to data management moving forward. Whether you're manipulating data on client or server side, these newly added native methods are much welcomed.

Recent Features

  • 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...

  • 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?

Incredible Demos

  • By
    MooTools Overlay Plugin

    Overlays have become a big part of modern websites; we can probably attribute that to the numerous lightboxes that use them. I've found a ton of overlay code snippets out there but none of them satisfy my taste in code. Many of them are...

  • By
    Parallax Sound Waves Animating on Scroll

    Scrolling animations are fun. They are fun to create and fun to use. If you are tired of bootstrapping you might find playing with scrolling animations as a nice juicy refreshment in your dry front-end development career. Let's have a look how to create animating...

Discussion

  1. The groupToMap() example might have an error – it’s still calling group()

    I didn’t know about these functions though, very useful!

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