Check for Subarray in JavaScript
Last Updated :
23 Jul, 2025
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.
