Array.length

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 20157.

length Array 32

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

// returns 4

var namelistA = new Array(4294967296); //2^32 = 4294967296
var namelistC = new Array(-100); //

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; // 0 ~ 2^32 -1
console.log(namelistB.length);

//4294967295

length length array.length 2 3 3 (non-iterable)(empty slot)

const arr = [1, 2];
console.log(arr);
// [ 1, 2 ]

arr.length = 5; // arrlength25
console.log(arr);
// [ 1, 2, <3 empty items> ]

arr.forEach(element => console.log(element)); // 
// 1
// 2

length length

`Array.length`

Writable: false
Configurable: false(Writable, Configurable, or Enumerable)
Enumerable: true for for..in

, numbers length

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

, numbers 3 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

Specification
ECMAScript 2027 LanguageSpecification # sec-properties-of-array-instances-length

Array

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Array.length

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