Lodash's `filter()` Function

Lodash’s `filter()` Function

In this post, we will give you information about Lodash’s `filter()` Function. Here we will give you detail about Lodash’s `filter()` Function And how to use it also give you a demo for it if it is necessary.

Given an array arr, Lodash’s filter() function returns an array containing all the elements in arr for which the function returned a truthy value.

const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];

_.filter(arr, isEven); // [2, 4, 6, 8]
function isEven(v) { return v % 2 === 0; }

The function you pass to filter() is called the predicate. If the predicate returns a falsy value (like null, undefined, , or ''), Lodash filters that value out.

const arr = [null, false, 0, 'hello'];

_.filter(arr, v => v); // ['hello']

On Arrays of Objects for Lodash’s `filter()` Function

The filter() function has a couple convenient shorthands for dealing with arrays of objects. If you pass a string predicate
instead of a function, Lodash will filter by whether that property is truthy or falsy.

const arr = [
  {},
  { hello: null },
  { hello: false },
  { hello: 0 },
  { hello: 'world' }
];

_.filter(arr, 'hello'); // [{ hello: 'world' }]

If your predicate is an object obj, Lodash will filter objects that match the given predicate. In other words, Lodash will match objects that have the same value as obj for all properties in obj.

const arr = [
  { firstName: 'Will', lastName: 'Riker', rank: 'Commander' },
  { firstName: 'Beverly', lastName: 'Crusher', rank: 'Commander' },
  { firstName: 'Wesley', lastName: 'Crusher', rank: 'Ensign' }
];

// ['Riker', 'Crusher']
_.filter(arr, { rank: 'Commander' }).map(v => v.lastName);

// ['Beverly', 'Wesley']
_.filter(arr, { lastName: 'Crusher' }).map(v => v.firstName);

// ['Beverly']
_.filter(arr, { lastName: 'Crusher', rank: 'Commander' }).map(v => v.firstName);

On Objects

The _.filter() function can also accept an object as a parameter, rather than an array. Calling _.filter(obj, fn) behaves similarly
to _.filter(Object.values(obj), fn).

const obj = {
  one: 1,
  two: 2,
  three: 3,
  four: 4
};
_.filter(obj, v => v % 2 === 0); // [2, 4]