JavaScript - get unique random elements from array (unique indexes)

In this article, we would like to show you how to get unique random elements from an array in JavaScript.

Practical example

In this example, we create a reusable function that gets unique random elements from an array (by index).

To get items with random indexes we use the Math.random() method and to ensure their uniqueness we use Set.

// ONLINE-RUNNER:browser;

const randomizeIndex = (count) => {
    return Math.floor(count * Math.random());
};

const randomizeElemnts = (array, count) => {
    if (count > array.length) {
        throw new Error('Array size cannot be smaller than expected random numbers count.');
    }
    const result = [];
    const guardian = new Set();
    while (result.length < count) {
        const index = randomizeIndex(count);
        if (guardian.has(index)) {
            continue;
        }
        const element = array[index];
        guardian.add(index);
        result.push(element);
    }
    return result;
};


// Usage example:

const array = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
const element = randomizeElemnts(array, 5);

console.log(element);  // Example output: [2, 0, 4, 3, 1]

See also

1. JavaScript - get multiple random elements from array

2. JavaScript - get unique random values from array

References

1. Math.random() - JavaScript | MDN
2. Math.floor() - JavaScript | MDN
3. Set.prototype.has() - JavaScript | MDN
4. Set.prototype.add() - JavaScript | MDN