mozilla
Your Search Results

    Array.prototype.every()

    Summary

    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
    The current element being processed in the array.
    index
    The index of the current element being processed in the array.
    array
    The array every was called upon.
    thisArg
    Optional. Value to use as this when executing callback.

    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

    Example: 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
    

    Example: 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 6 (ECMA-262)
    The definition of 'Array.prototype.every' in that specification.
    Release Candidate  

    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)

    See also

    Hide Sidebar