JavaScript Program to Create an Array with a Specific Length and Pre-filled Values

In JavaScript, we can create an array with a specific length and pre-filled values using various approaches. This can be useful when we need to initialize an array with default or placeholder values before populating it with actual data.

Method 1: Using the Array() Constructor and fill() Method

The Array constructor can be used to create an array of a specific length. The fill() method can fill this array with a specified value.

Syntax:

const filledArray = new Array(length).fill(value);

Example: Below is the implementation of the above approach

Javascript

const length = 5;
const value = 5;
const filledArray = new Array(length).fill(value);
console.log(filledArray);

Output

[ 5, 5, 5, 5, 5 ]

Method 2: Using a Loop to Initialize Values

We can use a loop to iterate through the desired length and assign values.

Syntax:

const filledArray = Array.from();
for (let i = 0; i < length; i++) {
    filledArray.push(value);
}

Example: Below is the implementation of the above approach

Javascript

const length = 5;
const filledArray = new Array();
for (let i = 0; i < length; i++) {
    filledArray.push(i + 1);
}
console.log(filledArray);

Output

[ 1, 2, 3, 4, 5 ]

Method 3: Using the map() Method

The map() method can be used to create an array by applying a function to each element.

Syntax:

const filledArray = Array.from({ length }).map(() => value);

Example: Below is the implementation of the above approach

Javascript

const length = 5;
const filledArray =
    Array.from({ length })
        .map(() => 5);
console.log(filledArray);

Output

[ 5, 5, 5, 5, 5 ]