Reverse an array in different ways.

There is a built-in array method in Javascript that reverses the array i.e. reverse() method. 1. Using reverse() method: reverse() method: The reverse() method reverses the array in place, meaning it modifies the original array directly and does not return a new array. Example: const givenArr = [5, 2, 3, 7, 9, 15, 20]; const reversedArr1 = givenArr.reverse(); // Prints the reversed array console.log(reversedArr1); // Output: [20, 15, 9, 7, 3, 2, 5] console.log(givenArr); // Output: [20, 15, 9, 7, 3, 2, 5] The reverse() method directly modifies the original array by reversing its elements. The reversed array is also returned as the result of the method In the above example, If you want to avoid modifying the original array, you can first create a copy of the array using .slice() and then apply .reverse() to the copy. const givenArr = [5, 2, 3, 7, 9, 15, 20]; // Create a copy of the array and reverse the copy const reversedArr = givenArr.slice().reverse(); console.log(reversedArr); // Output: [20, 15, 9, 7, 3, 2, 5] console.log(givenArr); // Output: [5, 2, 3, 7, 9, 15, 20] 2. Using a for-loop: const givenArr = [5, 12, 3, 7, 21, 9, 45, 90]; const printReversedArr = (arr) => { const arrLen = arr.length; for(let i = 0; i < arrLen / 2; i++) { let temp = arr[i]; arr[i] = arr[arrLen - 1 - i]; arr[arrLen - 1 - i] = temp } return arr ; } console.log(printReversedArr(givenArr)); // Output: [90, 45, 9, 21, 7, 3, 12, 5] 3. Using a for-loop (with a new array): const givenArr = [5, 12, 3, 7, 21, 9, 45, 90]; const getReverseArr = (arr) => { let reversedArr = []; for(let i = arr.length - 1; i >= 0 ; i --) { reversedArr.push(arr[i]); } return reversedArr; } console.log(getReverseArr(givenArr)); // Output: [90, 45, 9, 21, 7, 3, 12, 5] 4. Using forEach() method: const givenArr = [ 12, 3, 21, 9, 45, 22, 7]; const reverseArray = (arr) => { let reversedArr = []; arr.forEach(item => { reversedArr.unshift(item); }); return reversedArr; } console.log(reverseArray(givenArr)); // Output: [7, 22, 45, 9, 21, 3, 12] 5. Using reduce() method: const givenArr = [ 12, 3, 21, 9, 45, 22, 7]; const reverseArray = (arr) => { return arr.reduce((reversed, current) => [current, ...reversed], []); } console.log(reverseArray(givenArr)); // Output: [7, 22, 45, 9, 21, 3, 12] 6. Using unshift() method: const givenArr = [5, 2, 3, 7, 9, 15, 20]; const reverseArray = (arr) => { let reversedArr = []; for (let i = 0; i < arr.length; i++) { reversedArr.unshift(arr[i]); } return reversedArr; } console.log(reverseArray(givenArr)); // Output: [20, 15, 9, 7, 3, 2, 5] 7. Using a while loop (in-place modification): const givenArr = [10, 6, 9, 3, 4, 5, 1]; const reverseArray = (arr) => { let start = 0; let end = arr.length - 1; while (start < end) { // Swap elements at start and end let temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } return arr; } console.log(reverseArray(givenArr)); // Output: [1, 5, 4, 3, 9, 6, 10] 8. Using recursion: const givenArr = [10, 6, 9, 3, 4, 5, 1]; const reverseArray = (arr) => { if (arr.length === 0) { return arr; } else { return reverseArray(arr.slice(1)).concat(arr[0]); } } console.log(reverseArray(givenArr)); // Output: [1, 5, 4, 3, 9, 6, 10] console.log("Original Array: ", givenArr); // Output: Original Array: [10, 6, 9, 3, 4, 5, 1]

Feb 6, 2025 - 11:43

There is a built-in array method in Javascript that reverses the array i.e. reverse() method.

1. Using reverse() method:

reverse() method: The reverse() method reverses the array in place, meaning it modifies the original array directly and does not return a new array.

Example:

const givenArr = [5, 2, 3, 7, 9, 15, 20];
const reversedArr1 = givenArr.reverse();

// Prints the reversed array
console.log(reversedArr1);  // Output: [20, 15, 9, 7, 3, 2, 5]
console.log(givenArr);  // Output: [20, 15, 9, 7, 3, 2, 5]

The reverse() method directly modifies the original array by reversing its elements.
The reversed array is also returned as the result of the method

In the above example, If you want to avoid modifying the original array, you can first create a copy of the array using .slice() and then apply .reverse() to the copy.

const givenArr = [5, 2, 3, 7, 9, 15, 20];

// Create a copy of the array and reverse the copy
const reversedArr = givenArr.slice().reverse();

console.log(reversedArr);  // Output: [20, 15, 9, 7, 3, 2, 5]
console.log(givenArr);   // Output: [5, 2, 3, 7, 9, 15, 20]

2. Using a for-loop:

const givenArr = [5, 12, 3, 7, 21, 9, 45, 90];
const printReversedArr = (arr) => {
    const arrLen = arr.length;
    for(let i = 0; i < arrLen / 2; i++) {
        let temp = arr[i];
        arr[i] = arr[arrLen - 1 - i];
        arr[arrLen - 1 - i] = temp
    }
    return arr ;
}
console.log(printReversedArr(givenArr));  // Output: [90, 45, 9, 21, 7, 3, 12, 5]

3. Using a for-loop (with a new array):

const givenArr = [5, 12, 3, 7, 21, 9, 45, 90];
const getReverseArr = (arr) => {
    let reversedArr = [];
    for(let i = arr.length - 1; i >= 0 ; i --) {
        reversedArr.push(arr[i]);
    }
    return reversedArr;
}
console.log(getReverseArr(givenArr));  // Output: [90, 45, 9, 21, 7, 3, 12, 5]

4. Using forEach() method:

const givenArr = [ 12, 3, 21, 9, 45, 22, 7];
const reverseArray = (arr) => {
    let reversedArr = [];
    arr.forEach(item => {
        reversedArr.unshift(item);
    });
    return reversedArr;
}
console.log(reverseArray(givenArr));  // Output: [7, 22, 45, 9, 21, 3, 12]

5. Using reduce() method:

const givenArr = [ 12, 3, 21, 9, 45, 22, 7];
const reverseArray = (arr) => {
    return arr.reduce((reversed, current) => [current, ...reversed], []);
}
console.log(reverseArray(givenArr));  // Output: [7, 22, 45, 9, 21, 3, 12]

6. Using unshift() method:

const givenArr = [5, 2, 3, 7, 9, 15, 20];
const  reverseArray = (arr) => {
    let reversedArr = [];
    for (let i = 0; i < arr.length; i++) {
        reversedArr.unshift(arr[i]);
    }
    return reversedArr;
}
console.log(reverseArray(givenArr));  // Output: [20, 15, 9, 7, 3, 2, 5]

7. Using a while loop (in-place modification):

const givenArr = [10, 6, 9, 3, 4, 5, 1];
const reverseArray = (arr) => {
    let start = 0;
    let end = arr.length - 1;
    while (start < end) {
        // Swap elements at start and end
        let temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;

        start++;
        end--;
    }
    return arr;
}
console.log(reverseArray(givenArr));  // Output: [1, 5, 4, 3, 9, 6, 10]

8. Using recursion:

const givenArr = [10, 6, 9, 3, 4, 5, 1];
const reverseArray = (arr) =>  {
    if (arr.length === 0) {
        return arr;
    } else {
        return reverseArray(arr.slice(1)).concat(arr[0]);
    }
}
console.log(reverseArray(givenArr));  // Output: [1, 5, 4, 3, 9, 6, 10]
console.log("Original Array: ", givenArr);  // Output: Original Array: [10, 6, 9, 3, 4, 5, 1]