JavaScript Array.fill() Method Example

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The fill() method fills (modifies) all the elements of an array from a start index (default zero) to an end index (default array length) with a static value. It returns the modified array.

Syntax

arr.fill(value[, start[, end]])

• value - Value to fill an array.
• start - Optional. Start index, defaults to 0.
• end - Optional. End index defaults to this.length.

Examples

Example 1: Simple Array.fill() Method Example

var array1 = [1, 2, 3, 4];

// fill with 0 from position 2 until position 4
console.log(array1.fill(0, 2, 4));
// fill with 5 from position 1
console.log(array1.fill(5, 1));
console.log(array1.fill(6));

Output:

[1, 2, 0, 0]
[1, 5, 5, 5]
[6, 6, 6, 6]

More Examples

[1, 2, 3].fill(4);               // [4, 4, 4]
[1, 2, 3].fill(4, 1);            // [1, 4, 4]
[1, 2, 3].fill(4, 1, 2);         // [1, 4, 3]
[1, 2, 3].fill(4, 1, 1);         // [1, 2, 3]
[1, 2, 3].fill(4, 3, 3);         // [1, 2, 3]
[1, 2, 3].fill(4, -3, -2);       // [4, 2, 3]
[1, 2, 3].fill(4, NaN, NaN);     // [1, 2, 3]
[1, 2, 3].fill(4, 3, 5);         // [1, 2, 3]
Array(3).fill(4);                // [4, 4, 4]
[].fill.call({ length: 3 }, 4);  // {0: 4, 1: 4, 2: 4, length: 3}

// Objects by reference.
var arr = Array(3).fill({}) // [{}, {}, {}];
arr[0].hi = "hi"; // [{ hi: "hi" }, { hi: "hi" }, { hi: "hi" }]