Array.length

The array length property sets or returns the number of elements in an array. It represents an unsigned, 32-bit integer that is always numerically greater than the highest index in the array.

var items = ['shoes', 'shirts', 'socks', 'sweaters'];
items.length; 

// returns 4

Description

The value of the length property is an integer with a positive sign and a value less than 2 to the 32nd power (2³²).

You can set the length property to truncate an array at any time. When you extend an array by changing its length property, the number of actual elements does not increase; for example, if you set length to 3 when it is currently 2, the array still contains only 2 elements. Thus, the length property does not necessarily indicate the number of defined values in the array. See also Relationship between length and numerical properties.

Property attributes of Array.length
Writable	yes
Enumerable	no
Configurable	no

Examples

Iterating over an array

In the following example, the array numbers is iterated through by looking at the length property. The value in each element is then doubled.

var numbers = [1, 2, 3, 4, 5];
var length = numbers.length;
for (var i = 0; i < length; i++) {
  numbers[i] *= 2;
}
// numbers is now [2, 4, 6, 8, 10]

Shortening an array

The following example shortens the array numbers to a length of 3 if the current length is greater than 3.

var numbers = [1, 2, 3, 4, 5];

if (numbers.length > 3) {
  numbers.length = 3;
}

console.log(numbers); // [1, 2, 3]
console.log(numbers.length); // 3

Specifications

Specification	Status	Comment
ECMAScript 1st Edition (ECMA-262)	Standard	Initial definition.
ECMAScript 5.1 (ECMA-262) The definition of 'Array.length' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.length' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'Array.length' in that specification.	Draft

Browser compatibility

See also

• Array