Array.length

The length property of an object which is an instance of type Array sets or returns the number of elements in that array. The value is 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).

var namelistA = new Array(4294967296); //2 to the 32nd power = 4294967296 
var namelistC = new Array(-100) //negative sign
console.log(namelistA.length); //RangeError: Invalid array length 
console.log(namelistC.length); //RangeError: Invalid array length 
var namelistB = []; 
namelistB.length = Math.pow(2,32)-1; //set array length less than 2 to the 32nd power 
console.log(namelistB.length); 
//4294967295

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.

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

Browser compatibility

See also

• Array