DEV Community

Cover image for #LearnedToday: Object.groupBy()
Daniel Zotti
Daniel Zotti

Posted on

#LearnedToday: Object.groupBy()

🥳 It is finally out! No more need to write ugly code to group an array of objects by a specific value of a field!

Since late 2023, there is an official static method for Object called groupBy() that does it for us!
It accepts an Iterable, such as an Array, and a function, which is executed for each element and must return the "category" of that specific element.
The method returns a new Object where each key is a different category that contains an array of objects belonging to that specific category.

NOTE: The elements in the returned object and the original iterable are the same (not deep copies!). Changing the internal structure of the elements will be reflected in both the original iterable and the returned object.

Example

Let's give a practical example to see how easy it is to group all the Ninja Turtles characters by age.

The initial Array

const ninjaTurtlesCharacters = [
  { age: 16, name: 'Michelangelo' },
  { age: 16, name: 'Raffaello' },
  { age: 16, name: 'Donatello' },
  { age: 16, name: 'Leonardo' },
  { age: 91, name: 'Splinter' },
  { age: 25, name: 'Casey Jones' },
  { age: 25, name: 'April O\'Neil' }
];
Enter fullscreen mode Exit fullscreen mode

The good OLD way (with reduce)

const ninjaTurtlesCharactersByAge = ninjaTurtlesCharacters.reduce(
  (groupedPeople, item) => ({
    ...groupedPeople,
    [item.age]: groupedPeople[item.age]
      ? [...groupedPeople[item.age], item]
      : [item],
  }),
  {}
);
Enter fullscreen mode Exit fullscreen mode

The MODERN way

const ninjaTurtlesCharactersByAgeNew = Object.groupBy(
  ninjaTurtlesCharacters,
  ({ age }) => age
);
Enter fullscreen mode Exit fullscreen mode

Tip: use Map.groupBy() if you want to return a Map instead of an Object

The result

{
  "16": [
    { age: 16, name: 'Michelangelo' },
    { age: 16, name: 'Raffaello' },
    { age: 16, name: 'Donatello' },
    { age: 16, name: 'Leonardo' }
  ],
  "25": [
    { age: 25, name: 'Casey Jones' },
    { age: 25, name: 'April O\'Neil' }
  ],
  "91": [
    { age: 91, name: 'Splinter' }
  ]
}
Enter fullscreen mode Exit fullscreen mode

Demo

🧑🏻‍💻 As usual, I created a simple Stackblitz prject to play with the code.

🗄 Docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/groupBy

ℹ Browser support: https://caniuse.com/mdn-javascript_builtins_object_groupby

Sentry blog image

How I fixed 20 seconds of lag for every user in just 20 minutes.

Our AI agent was running 10-20 seconds slower than it should, impacting both our own developers and our early adopters. See how I used Sentry Profiling to fix it in record time.

Read more

Top comments (0)

AWS Security LIVE!

Tune in for AWS Security LIVE!

Join AWS Security LIVE! for expert insights and actionable tips to protect your organization and keep security teams prepared.

Learn More

👋 Kindness is contagious

Explore a sea of insights with this enlightening post, highly esteemed within the nurturing DEV Community. Coders of all stripes are invited to participate and contribute to our shared knowledge.

Expressing gratitude with a simple "thank you" can make a big impact. Leave your thanks in the comments!

On DEV, exchanging ideas smooths our way and strengthens our community bonds. Found this useful? A quick note of thanks to the author can mean a lot.

Okay