JavaScript Tutorials

JavaScript Array fill()
Syntax & Examples

Array.fill() method

The fill() method of the Array class in JavaScript fills all the elements of an array from a start index to an end index with a static value. This method modifies the original array.

Syntax of Array.fill()

There are 3 variations for the syntax of Array.fill() method. They are:

1.
fill(value)

Parameters

ParameterOptional/RequiredDescription
valuerequiredThe value to fill the array with.

This method fills all the elements of an array with a static value.

Returns value of type Array.

2.
fill(value, start)

Parameters

ParameterOptional/RequiredDescription
valuerequiredThe value to fill the array with.
startoptionalThe start index, defaults to 0.

This method fills all the elements of an array from the start index with a static value.

Returns value of type Array.

3.
fill(value, start, end)

Parameters

ParameterOptional/RequiredDescription
valuerequiredThe value to fill the array with.
startoptionalThe start index, defaults to 0.
endoptionalThe end index, defaults to the array's length.

This method fills all the elements of an array from the start index to the end index with a static value.

Returns value of type Array.


✐ Examples

1 Using fill() method to fill an entire array

In JavaScript, we can use the fill() method to fill all the elements of an array with a static value.

For example,

  1. We define an array variable arr with elements [1, 2, 3, 4, 5].
  2. We use the fill() method with the value 0 to fill the entire array with 0.
  3. The resulting array is modified in place.
  4. We log the array to the console using console.log() method to see the filled array.

JavaScript Program

const arr = [1, 2, 3, 4, 5];
arr.fill(0);
console.log(arr);

Output

[0, 0, 0, 0, 0]

2 Using fill() method to fill an array from a start index

We can use the fill() method to fill elements of an array from a specified start index with a static value.

For example,

  1. We define an array variable arr with elements ['a', 'b', 'c', 'd', 'e'].
  2. We use the fill() method with the value 'x' and the start index 2 to fill the array from index 2 with 'x'.
  3. The resulting array is modified in place.
  4. We log the array to the console using console.log() method to see the filled array.

JavaScript Program

const arr = ['a', 'b', 'c', 'd', 'e'];
arr.fill('x', 2);
console.log(arr);

Output

['a', 'b', 'x', 'x', 'x']

3 Using fill() method to fill an array from a start index to an end index

We can use the fill() method to fill elements of an array from a specified start index to an end index with a static value.

For example,

  1. We define an array variable numArr with elements [1, 2, 3, 4, 5].
  2. We use the fill() method with the value 9, the start index 1, and the end index 3 to fill the array from index 1 to 3 with 9.
  3. The resulting array is modified in place.
  4. We log the array to the console using console.log() method to see the filled array.

JavaScript Program

const numArr = [1, 2, 3, 4, 5];
numArr.fill(9, 1, 3);
console.log(numArr);

Output

[1, 9, 9, 4, 5]

Summary

In this JavaScript tutorial, we learned about fill() method of Array: the syntax and few working examples with output and detailed explanation for each example.