How to Create an Array Containing 1…N in JavaScript?

In JavaScript, there are several ways to create an array containing numbers from 1 to N.

1. Using a for Loop

The basic method is to create an array of numbers is by using a for loop.

function createArray(n) {
    let arr = [];
    for (let i = 1; i <= n; i++) {
        arr.push(i);
    }
    return arr;
}

// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(createArray(10));

Explanation

• Step 1: Initialize an empty array arr.
• Step 2: Use a for loop starting at 1 and ending at N.
• Step 3: Push each number into the array.
• Step 4: The array is returned after the loop completes.

2. Using Array.from() Method

The Array.from() method creates a new array from an array-like or iterable object. It can be useful for generating arrays with numbers in a given range.

 function createArray(n) {
    return Array.from({ length: n }, (_, index) => index + 1);
}

// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(createArray(10));

Explanation

• Step 1: We use Array.from() with an object { length: n } to define the size of the array.
• Step 2: The second argument is a mapping function that takes the current element (ignored with _) and the index. We add 1 to the index to start the array from 1.

3. Using map() with Array() Methods

You can use the map() method on a newly created array. By combining it with the Array() constructor, we can create an array with a specified length and then populate it with numbers.

function createArray(n) {
    return [...Array(n)].map((_, index) => index + 1);
}

// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(createArray(10));

Explanation

• Step 1: […Array(n)] creates an array of length n with empty slots.
• Step 2: We use the .map() method to iterate over each slot, and the index argument provides the current index, which we increment by 1 to get the numbers starting from 1.

4. Using Array.fill() and map() Method

This approach combines the Array.fill() method with map() to generate an array containing numbers from 1 to N. It’s another concise and elegant method.

Code Example:

function createArray(n) {
    return new Array(n).fill().map((_, index) => index + 1);
}

// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(createArray(10));

Explanation

• Step 1: new Array(n).fill() creates an empty array of length n and fills it with undefined.
• Step 2: .map() is used to iterate through the array, and the index is incremented by 1 to get the numbers starting from 1.

5. Using while Loop

If you prefer a while loop over a for loop, you can achieve the same result with this approach. Although less common for this kind of task, it’s still a valid method.

function createArray(n) {
    let arr = [];
    let i = 1;
    
    while (i <= n) {
        arr.push(i);
        i++;
    }
    return arr;
}

// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(createArray(10));

Explanation

• Step 1: Initialize an empty array arr and a counter i starting at 1.
• Step 2: The while loop continues as long as i is less than or equal to n.
• Step 3: Each iteration adds the value of i to the array and increments it by 1.
• Step 4: The final array is returned after the loop ends.