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Check for Subarray in JavaScript

Last Updated : 23 Jul, 2025
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Here are the different approaches to check for Subarray in JavaScript

Using String Conversion with join() - Best Method

This approach converts both arrays into strings and checks if the subarray string is contained within the master array string.

JavaScript 
function checkSub(a, sub) {
    return a.join(',').includes(sub.join(','));
}

let a = [12, 44, 22, 66, 222, 777, 22, 22, 22, 6, 77, 3]
console.log(checkSub(a, [777, 22, 22]));

Output

true

Using a Closure with indexOf()

This approach uses a closure to keep track of the index for searching within the master array. It ensures that the elements of the subarray appear in the same order within the master array.

JavaScript 
function subArray(a, sub) {
    return sub.every((i => v => i = a.indexOf(v, i) + 1)(0));
}

const a = [12, 44, 22, 66, 222, 777, 22, 22, 22, 6, 77, 3];
console.log(subArray(a, [777, 22, 22]));

Output

true

Sliding Window Technique

This approach slides over the master array using a window that matches the size of the subarray and checks for element-wise equality.

JavaScript 
function subArray(a, sub) {
    const subLength = sub.length;
    for (let i = 0; i <= a.length - subLength; i++) {
        let isMatch = true;
        for (let j = 0; j < subLength; j++) {
            if (a[i + j] !== sub[j]) {
                isMatch = false;
                break;
            }
        }
        if (isMatch) return true;
    }
    return false;
}

let a = [12, 44, 22, 66, 222, 777, 22, 22, 22, 6, 77, 3]
console.log(subArray(a, [777, 22, 22]));

Output

true

Using Functional Approach

This approach uses Array.prototype.every() combined with indexOf() to ensure the order is preserved while checking for elements.

JavaScript 
function isSubArray(main, sub) {
    let index = -1;
    return sub.every(
        (element) => (index = main.indexOf(element, index + 1)) !== -1
    );
}

const a = [12, 44, 22, 66, 222, 777, 22, 22, 22, 6, 77, 3];
console.log(isSubArray(a, [777, 22, 22]));

Output

true

Which Approach To Use?

  • String Conversion: Best Method in terms of efficiency and usage
  • Closure with indexOf(): Best for simple subarray checks with order preservation.
  • Functional Approach: Concise and maintains order.
  • Sliding Window: More robust and efficient for large arrays with repeated elements.

S

souravsharma098
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