How to Shuffle Arrays in JavaScript

Shuffling arrays in JavaScript can be efficiently done using the Fisher-Yates (or Knuth) shuffle algorithm. This algorithm ensures a uniform random shuffle and operates in linear time, O(n), making it suitable for shuffling arrays of any size. Here’s how you can implement it:

Fisher-Yates Shuffle Algorithm#

1. Initialize: Start with the last element of the array.
2. Swap: For each element, swap it with a randomly chosen element that comes before or at the current position.
3. Repeat: Continue this process until the first element is reached.

Code Example#

Here’s a concise implementation of the Fisher-Yates shuffle algorithm in JavaScript:

function shuffleArray(array) {
    for (let i = array.length - 1; i > 0; i--) {
        // Generate a random index from 0 to i
        const j = Math.floor(Math.random() * (i + 1));

        // Swap elements at indices i and j
        [array[i], array[j]] = [array[j], array[i]];
    }
    return array;
}

// Example usage:
const myArray = [1, 2, 3, 4, 5];
console.log("Original array:", myArray);

const shuffledArray = shuffleArray(myArray);
console.log("Shuffled array:", shuffledArray);

Explanation#

• Loop: The loop runs from the end of the array (array.length - 1) down to the beginning (0).
• Random Index: Math.random() * (i + 1) generates a random number between 0 and i, and Math.floor() ensures it’s an integer.
• Swap: The destructuring assignment [array[i], array[j]] = [array[j], array[i]] swaps the elements at indices i and j.

Key Points#

• Uniformity: The Fisher-Yates shuffle algorithm guarantees that every permutation of the array is equally likely.
• Efficiency: It runs in O(n) time complexity, which is optimal for shuffling arrays.
• In-place: This algorithm shuffles the array in place without requiring extra space.

Feel free to use and modify this implementation as needed for your projects!