Array.prototype.every()

Με τη μέθοδο every() ελέγχονται όλα τα στοιχεία του πίνακα για το εάν περνούν το τεστ της συνάρτησης που ορίζετε.

Ο πηγαίος κώδικας για αυτό το διαδραστικό παράδειγμα βρίσκεται αποθηκευμένος σε ένα repository του GitHub. Εάν θέλετε να συνδράμετε στα διαδραστικά παραδείγματα, παρακαλώ κάντε clone το https://github.com/mdn/interactive-examples και στείλτε μας ένα pull request.

Συντακτικό

arr.every(callback(element[, index[, array]])[, thisArg])

Παράμετροι

callback

Συνάρτηση που ελέγχει κάθε στοιχείο, δέχεται τρία ορίσματα.

element (απαιτείται)

Το αντικείμενο που επεξεργαζόμαστε στον πίνακα.

indexOptional

Ο δείκτης του τρέχοντος στοιχείου του πίνακα που βρίσκεται υπό επεξεργασία.

arrayOptional

Ο πίνακας πάνω στο οποίο καλείται η μέθοδος every().

thisArgOptional

Προαιρετικό. Τιμή που χρησιμοποιείται σαν this όταν εκτελείται το callback

Επιστρεφόμενη τιμή

true εάν η callback συνάρτηση επιστρέφει μια truthy τιμή για κάθε στοιχείο του πίνακα, αλλιώς false.

Περιγραφή

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. 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. 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 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. 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

Testing every object of an array for a value

[{a:1, b:2, c:3, d:4}, {a:1, x:2, y:3, z:4}, {a:1, x:2, y:3, z:4}].every(obj => obj.a === 1); //true
[{a:1, b:2, c:3, d:4}, {a:1, x:2, y:3, z:4}, {a:2, x:2, y:3, z:4}].every(obj => obj.a === 1); //false

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

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

Browser compatibility

See also

• Array.prototype.forEach()
• Array.prototype.some()
• TypedArray.prototype.every()