我們的志工尚未將此文章翻譯為 正體中文 (繁體) 版本。加入我們,幫忙翻譯!
The every()
method tests whether all elements in the array pass the test implemented by the provided function.
Syntax
arr.every(callback[, thisArg])
Parameters
callback
- Function to test for each element, taking three arguments:
currentValue
(required)- 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. 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 one where callback
returns a falsy value (a value that becomes false when converted to a Boolean). If such an element is found, the every
method immediately returns false
. Otherwise, if callback
returned a true value for all elements, every
will return 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.
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 passed to callback
when invoked, for use as its this
value. Otherwise, the value undefined
will be passed for use 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
. Elements which are appended to the array after the call to every
begins will not be visited by callback
. 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.)
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(elem => elem >= 10); // false [12, 54, 18, 130, 44].every(elem => elem >= 10); // true
Polyfill
every
was added to the ECMA-262 standard in the 5th edition; as such 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') { 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) { // 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 and argument list // containing kValue, k, and O. var testResult = callbackfn.call(T, kValue, k, O); // iii. If ToBoolean(testResult) is false, return false. if (!testResult) { return false; } } k++; } return true; }; }
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 5.1 (ECMA-262) The definition of 'Array.prototype.every' in that specification. |
Standard | Initial definition. Implemented in JavaScript 1.6. |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.prototype.every' in that specification. |
Standard | |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Array.prototype.every' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | 1.5 (1.8) | 9 | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | 1.0 (1.8) | (Yes) | (Yes) | (Yes) |