.groupBy()

The .groupBy() method groups items according to the value returned by a callback function. The return value of the .groupBy() method is a null-prototype object that doesn’t inherit any object methods.

Syntax

Object.groupBy(items, callfunc);

• items: It is an array. They will be grouped according to the result of the callfunc.
• callfunc: It is a callback function. This function returns a string or a symbol.

Example

In the following example, the code groups users by their subscription year:

const subs = [
  { userName: 'Lisa', yearSub: 2022 },
  { userName: 'Akim', yearSub: 2020 },
  { userName: 'Lola', yearSub: 2020 },
];

const subsByYear = Object.groupBy(subs, (user) => {
  return user.yearSub;
});

Note: To run this code, it is necessary to add a library like Lodash.

The output of the above code will be:

{
  '2020': [
    { userName: 'Akim', yearSub: 2020 },
    { userName: 'Lola', yearSub: 2020 }
  ],
  '2022': [ { userName: 'Lisa', yearSub: 2022 } ]
}