Lodash's `filter()` Function
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, 0, or ''), Lodash filters that value out.
const arr = [null, false, 0, 'hello'];
_.filter(arr, v => v); // ['hello']On Arrays of Objects
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]