The filter()
method creates a new array with all elements that pass the test implemented by the provided function.
var words = ["spray", "limit", "elite", "exuberant", "destruction", "present"]; var longWords = words.filter(function(word){ return word.length > 6; }); // Filtered array longWords is ["exuberant", "destruction", "present"]
Syntax
var newArray = arr.filter(callback[, thisArg])
Parameters
callback
- Function is a predicate, to test each element of the array. Return
true
to keep the element,false
otherwise, taking three arguments: -
element
- The current element being processed in the array.
index
- The index of the current element being processed in the array.
array
- The array
filter
was called upon.
thisArg Optional
- Optional. Value to use as
this
when executingcallback
.
Return value
A new array with the elements that pass the test.
Description
filter()
calls a provided callback
function once for each element in an array, and constructs a new array of all the values for which callback
returns a value that coerces to true
. callback
is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values. Array elements which do not pass the callback
test are simply skipped, and are not included in the new array.
callback
is invoked with three arguments:
- the value of the element
- the index of the element
- the Array object being traversed
If a thisArg
parameter is provided to filter
, it will be used as the callback's this
value. Otherwise, the value undefined
will be used as its this
value. The this
value ultimately observable by callback
is determined according to the usual rules for determining the this
seen by a function.
filter()
does not mutate the array on which it is called.
The range of elements processed by filter()
is set before the first invocation of callback
. Elements which are appended to the array after the call to filter()
begins will not be visited by callback
. If existing elements of the array are changed, or deleted, their value as passed to callback
will be the value at the time filter()
visits them; elements that are deleted are not visited.
Examples
Filtering out all small values
The following example uses filter()
to create a filtered array that has all elements with values less than 10 removed.
function isBigEnough(value) { return value >= 10; } var filtered = [12, 5, 8, 130, 44].filter(isBigEnough); // filtered is [12, 130, 44]
Filtering invalid entries from JSON
The following example uses filter()
to create a filtered json of all elements with non-zero, numeric id
.
var arr = [ { id: 15 }, { id: -1 }, { id: 0 }, { id: 3 }, { id: 12.2 }, { }, { id: null }, { id: NaN }, { id: 'undefined' } ]; var invalidEntries = 0; function isNumber(obj) { return obj!== undefined && typeof(obj) === 'number' && !isNaN(obj); } function filterByID(item) { if (isNumber(item.id)) { return true; } invalidEntries++; return false; } var arrByID = arr.filter(filterByID); console.log('Filtered Array\n', arrByID); // Filtered Array // [{ id: 15 }, { id: -1 }, { id: 0 }, { id: 3 }, { id: 12.2 }] console.log('Number of Invalid Entries = ', invalidEntries); // Number of Invalid Entries = 4
Searching in array
Following example uses filter() to filter array content based on search criteria
var fruits = ['apple', 'banana', 'grapes', 'mango', 'orange']; /** * Array filters items based on search criteria (query) */ function filterItems(query) { return fruits.filter(function(el) { return el.toLowerCase().indexOf(query.toLowerCase()) > -1; }) } console.log(filterItems('ap')); // ['apple', 'grapes'] console.log(filterItems('an')); // ['banana', 'mango', 'orange']
ES2015 Implementation
const fruits = ['apple', 'banana', 'grapes', 'mango', 'orange']; /** * Array filters items based on search criteria (query) */ const filterItems = (query) => { return fruits.filter((el) => el.toLowerCase().indexOf(query.toLowerCase()) > -1 ); } console.log(filterItems('ap')); // ['apple', 'grapes'] console.log(filterItems('an')); // ['banana', 'mango', 'orange']
Polyfill
filter()
was added to the ECMA-262 standard in the 5th edition; as such it may not be present in all implementations of the standard. You can work around this by inserting the following code at the beginning of your scripts, allowing use of filter()
in ECMA-262 implementations which do not natively support it. This algorithm is exactly equivelent to the one specified in ECMA-262, 5th edition, assuming that fn.call
evaluates to the original value of Function.prototype.bind()
, and that Array.prototype.push()
has its original value.
if (!Array.prototype.filter) Array.prototype.filter = function(func, thisArg) { 'use strict'; if ( ! ((typeof func === 'Function') && this) ) throw new TypeError(); var len = this.length >>> 0, res = new Array(len), // preallocate array c = 0, i = -1; if (thisArg === undefined) while (++i !== len) // checks to see if the key was set if (i in this) if (func(t[i], i, t)) res[c++] = t[i]; else while (++i !== len) // checks to see if the key was set if (i in this) if (func.call(thisArg, t[i], i, t)) res[c++] = t[i]; res.length = c; // shrink down array to proper size return res; };
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 5.1 (ECMA-262) The definition of 'Array.prototype.filter' in that specification. |
Standard | Initial definition. Implemented in JavaScript 1.6. |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.prototype.filter' in that specification. |
Standard | |
ECMAScript Latest Draft (ECMA-262) The definition of 'Array.prototype.filter' in that specification. |
Living Standard |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | 1.5 (1.8) | 9 | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Edge | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | 1.0 (1.8) | (Yes) | (Yes) | (Yes) |