JavaScript Array every() Method
The JavaScript Array.prototype.every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.
Syntax
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arr.every(callback(element[, index[, array]])[, thisArg])
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Parameters:
- callback: 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): Value to use as this when executing callback.
Description
The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.
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 returns a truthy value for all elements, every() returns true.
The 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.
Examples
Using every() to check all elements in an array are larger than 10:
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function isBigEnough(element, index, array) {
return element >= 10;
}
[12, 5, 8, 130, 44].every(isBigEnough); // false
[12, 54, 18, 130, 44].every(isBigEnough); // true
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Using every() with arrow function syntax:
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[12, 5, 8, 130, 44].every(x => x >= 10); // false [12, 54, 18, 130, 44].every(x => x >= 10); // true
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Browser Compatibility
The every() method is supported in all major browsers, including Internet Explorer 9 and higher.
Polyfill
If you need to support older browsers (like IE8 and below) you can use the following polyfill:
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if (!Array.prototype.every)
{
Array.prototype.every = function(fun /*, thisArg */)
{
'use strict';
if (this == null)
throw new TypeError();
var t = Object(this);
var len = t.length >>> 0;
if (typeof fun != 'function')
throw new TypeError();
var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
for (var i = 0; i < len; i++)
{
if (i in t && !fun.call(thisArg, t[i], i, t))
return false;
}
return true;
};
}
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