Array Properties (length)

The length property of an array returns the number of elements. It is a dynamic property; you can set it to truncate or extend the array. When you set a new length, the array is truncated or padded with empty slots.

Key Points

• length is an unsigned 32‑bit integer.
• Setting length to a smaller value removes elements beyond the new length.
• Setting length to a larger value adds empty slots (sparse array).
• The highest indexed element plus one determines the length.

Code Example

const arr = [10, 20, 30, 40];
console.log(arr.length); // 4

// Truncate
arr.length = 2;
console.log(arr); // [10, 20]

// Extend (creates empty slots)
arr.length = 5;
console.log(arr); // [10, 20, empty × 3]

// Accessing beyond length returns undefined
console.log(arr[4]); // undefined