Pluck values from and array of objects in JavaScript

Ever wanted to extract values from an array of objects based on a specific key? This is pretty common and can be achieved with a simple one-liner in JavaScript.

Pluck a single value for each object

All you need to do is use Array.prototype.map() to map the array of objects to the value of the specified key for each object.

const pluck = (arr, key) => arr.map(i => i[key]);

const simpsons = [
  { name: 'Lisa', age: 8, username: 'lisa_simpson' },
  { name: 'Homer', age: 36, username: 'homer_simpson' },
  { name: 'Marge', age: 34, username: 'marge_simpson' },
  { name: 'Bart', age: 10, username: 'bart_simpson' }
];

pluck(simpsons, 'age');
// [8, 36, 34, 10]

Pluck multiple values for each object

If you want to extract multiple values for each object, you can use a nested map() to iterate over the keys. This results in each object being mapped to an array of values.

const pluck = (arr, keys) => arr.map(i => keys.map(k => i[k]));

const simpsons = [
  { name: 'Lisa', age: 8, username: 'lisa_simpson' },
  { name: 'Homer', age: 36, username: 'homer_simpson' },
  { name: 'Marge', age: 34, username: 'marge_simpson' },
  { name: 'Bart', age: 10, username: 'bart_simpson' }
];

pluck(simpsons, ['name', 'age']);
// [['Lisa', 8], ['Homer', 36], ['Marge', 34], ['Bart', 10]]

Pluck any number of values for each object

Instead of having two separate functions for plucking a single value and multiple values, you can create a single function that accepts a variable number of keys. This way, you can pluck any number of values for each object.

In order to do so, you can use the rest argument syntax (...keys) to collect all the keys into an array. Then, you can check the length of the keys array to determine whether to return single or multiple values.

const pluck = (arr, ...keys) =>
  keys.length > 1 ?
    arr.map(i => keys.map(k => i[k])) :
    arr.map(i => i[keys[0]]);

const simpsons = [
  { name: 'Lisa', age: 8, username: 'lisa_simpson' },
  { name: 'Homer', age: 36, username: 'homer_simpson' },
  { name: 'Marge', age: 34, username: 'marge_simpson' },
  { name: 'Bart', age: 10, username: 'bart_simpson' }
];

pluck(simpsons, 'age');
// [8, 36, 34, 10]

pluck(simpsons, 'name', 'age');
// [['Lisa', 8], ['Homer', 36], ['Marge', 34], ['Bart', 10]]