The every()
method tests whether
all elements in the array pass the test implemented by the provided function. It
returns a Boolean value.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Syntax
arr.every(callback(element[, index[, array]])[, thisArg])
Parameters
callback
- A function to test for each element, taking three arguments:
element
- The current element being processed in the array.
index
Optional- The index of the current element being processed in the array.
array
Optional- The array
every
was called upon.
thisArg
Optional- A value to use as
this
when executingcallback
.
Return value
true
if the callback
function
returns a truthy value for every array element. Otherwise,
false
.
Description
The every
method executes the provided callback
function once for each element present in the array until it finds the one where
callback
returns a falsy value. If such an
element is found, the every
method immediately returns false
.
Otherwise, if callback
returns a truthy value
for all elements, every
returns true
.
Caution: Calling this method on an empty array will return
true
for any condition!
callback
is invoked only for array indexes which have assigned
values. It is not invoked for indexes which have been deleted, or which have never been
assigned values.
callback
is invoked with three arguments: the value of the
element, the index of the element, and the Array object being traversed.
If a thisArg
parameter is provided to every
, it
will be used as 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.
every
does not mutate the array on which it is called.
The range of elements processed by every
is set before the first
invocation of callback
. Therefore,
callback
will not run on elements that are appended to the array
after the call to every
begins. If existing elements of the array are
changed, their value as passed to callback
will be the value at
the time every
visits them. Elements that are deleted are not visited.
every
acts like the "for all" quantifier in mathematics. In particular,
for an empty array, it returns true
. (It is vacuously true that all
elements of the empty
set satisfy any given condition.)
Polyfill
every
was added to the ECMA-262 standard in the 5th edition,
and it may not be present in other implementations of the standard. You can work around
this by inserting the following code at the beginning of your scripts, allowing use of
every
in implementations which do not natively support it.
This algorithm is exactly the one specified in ECMA-262, 5th edition,
assuming Object
and TypeError
have their original values, and
that callbackfn.call
evaluates to the original value of
Function.prototype.call
.
if (!Array.prototype.every) {
Array.prototype.every = function(callbackfn, thisArg) {
'use strict';
var T, k;
if (this == null) {
throw new TypeError('this is null or not defined');
}
// 1. Let O be the result of calling ToObject passing the this
// value as the argument.
var O = Object(this);
// 2. Let lenValue be the result of calling the Get internal method
// of O with the argument "length".
// 3. Let len be ToUint32(lenValue).
var len = O.length >>> 0;
// 4. If IsCallable(callbackfn) is false, throw a TypeError exception.
if (typeof callbackfn !== 'function' && Object.prototype.toString.call(callbackfn) !== '[object Function]') {
throw new TypeError();
}
// 5. If thisArg was supplied, let T be thisArg; else let T be undefined.
if (arguments.length > 1) {
T = thisArg;
}
// 6. Let k be 0.
k = 0;
// 7. Repeat, while k < len
while (k < len) {
var kValue;
// a. Let Pk be ToString(k).
// This is implicit for LHS operands of the in operator
// b. Let kPresent be the result of calling the HasProperty internal
// method of O with argument Pk.
// This step can be combined with c
// c. If kPresent is true, then
if (k in O) {
var testResult;
// i. Let kValue be the result of calling the Get internal method
// of O with argument Pk.
kValue = O[k];
// ii. Let testResult be the result of calling the Call internal method
// of callbackfn with T as the this value if T is not undefined
// else is the result of calling callbackfn
// and argument list containing kValue, k, and O.
if(T) testResult = callbackfn.call(T, kValue, k, O);
else testResult = callbackfn(kValue,k,O)
// iii. If ToBoolean(testResult) is false, return false.
if (!testResult) {
return false;
}
}
k++;
}
return true;
};
}
Examples
Testing size of all array elements
The following example tests whether all elements in the array are bigger than 10.
function isBigEnough(element, index, array) {
return element >= 10;
}
[12, 5, 8, 130, 44].every(isBigEnough); // false
[12, 54, 18, 130, 44].every(isBigEnough); // true
Using arrow functions
Arrow functions provide a shorter syntax for the same test.
[12, 5, 8, 130, 44].every(x => x >= 10); // false
[12, 54, 18, 130, 44].every(x => x >= 10); // true
Affecting Initial Array (modifying, appending, and deleting)
The following examples tests the behavior of the every
method when the
array is modified.
// ---------------
// Modifying items
// ---------------
let arr = [1, 2, 3, 4];
arr.every( (elem, index, arr) => {
arr[index+1] -= 1
console.log(`[${arr}][${index}] -> ${elem}`)
return elem < 2
})
// Loop runs for 3 iterations, but would
// have run 2 iterations without any modification
//
// 1st iteration: [1,1,3,4][0] -> 1
// 2nd iteration: [1,1,2,4][1] -> 1
// 3rd iteration: [1,1,2,3][2] -> 2
// ---------------
// Appending items
// ---------------
arr = [1, 2, 3];
arr.every( (elem, index, arr) => {
arr.push('new')
console.log(`[${arr}][${index}] -> ${elem}`)
return elem < 4
})
// Loop runs for 3 iterations, even after appending new items
//
// 1st iteration: [1, 2, 3, new][0] -> 1
// 2nd iteration: [1, 2, 3, new, new][1] -> 2
// 3rd iteration: [1, 2, 3, new, new, new][2] -> 3
// ---------------
// Deleting items
// ---------------
arr = [1, 2, 3, 4];
arr.every( (elem, index, arr) => {
arr.pop()
console.log(`[${arr}][${index}] -> ${elem}`)
return elem < 4
})
// Loop runs for 2 iterations only, as the remaining
// items are `pop()`ed off
//
// 1st iteration: [1,2,3][0] -> 1
// 2nd iteration: [1,2][1] -> 2
Specifications
Browser compatibility
BCD tables only load in the browser