JavaScript Array.fill() Function

JavaScript Array.fill() Function | You can fill the array with a supplied static value using the Javascript arr.fill() method. You may utilize the value to fill the entire array or just a portion.

The syntax of the fill() method is:-
array.fill(value, start, end)

Changes all array elements from the ‘start’ to ‘end’ index to a static ‘value’ and returns the modified array. Passing start and end values are optional. Here:-

• value:- value to fill array section with.
• start:- index to start filling the array at. If the start is negative, it is treated as length+start where length is the length of the array.
• end:- index to stop filling the array at. If the end is negative, it is treated as length+end.

JavaScript Array.fill() Function Example-1

In JavaScript Array.fill() function passing start and end values are optional and in that case, all existing array elements will be replaced with the passed value.

let arr = [1, 453, 34, 68];
console.log("Original array: " + arr);

// fill array with 99
arr.fill(99);
console.log("New array: " + arr);

Output:-

Original array: 1, 453, 34, 68
New array: 99, 99, 99, 99

Array fill() JavaScript Function Example-2

In this example, the method fill() replaces all of the original values in the array by filling the array from index 1 to index 2, one less than the top index, with the value 90. The start and end indexes are exclusive in the filling operation.

let arr = [1, 453, 34, 68];
console.log("Original array: " + arr);

// here value = 90, start index=1 and
// and last index = 3
arr.fill(90, 1, 3);

console.log("New array: " + arr);

Output:-

Original array: 1, 453, 34, 68
New array: 1, 90, 90, 99

JavaScript Array.fill() Function Example-3

If we don’t pass the end index then the passed element will be filled from the start index to the end of the array i.e till the length-1 index.

let arr = [1, 453, 34, 68];
console.log("Original array: " + arr);

// here value = 90, start index=2 and
// and last index = arr.length
arr.fill(90, 2);

console.log("New array: " + arr);

Output:-

Original array: 1, 453, 34, 68
New array: 1, 453, 90, 90

JavaScript Array.fill() Function Example-4

All the above programs demonstrate filling elements when the array already contains some elements. Let us see an example when the array doesn’t contain elements.

let arr = new Array(5);
console.log("Original array: " + arr);
arr.fill(9);
console.log("Updated array: " + arr);

Output:-

Original array: ,,,,
Updated array: 9, 9, 9, 9, 9

Also see:- JavaScript Array shift() Function

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