Javascript Comparing Two Arrays

Comparing Two Arrays

In Javascript, array is a type of Object and Objects cannot be compared based on their values but of their references.

Convert to string and compare array

JSON.stringify()

We can convert the array into string and compare both using a equality operator

let arr1 = [1,3,5,7];
let arr2 = [1,3,5,7];
const compareTwoArrays = (a, b) => {
	return JSON.stringify(a) === JSON.stringify(b);
}
compareTwoArrays(arr1, arr2) // true

But in the above method, if one array contains null and another undefined then also it holds the comparison as true which is incorrect. So there other ways to make sure the comparison is accurate.

For loop

Let’s see how we can write a for loop to compare arrays.

function compareTwoArrays(a, b) {
	// Write a guard clause to check the length of both arrays
	if (a.length !== b.length) return false;
	for (let i = 0; i < a.length; i++) {
		if (a[i] !== b[i]){
			return false
		}
	}
	return true;
}
let arr1 = [1,3,5,7];
let arr2 = [1,3,5,7];
compareTwoArrays(arr1, arr2) // true
let arr1 = [1,3,5,7, null];
let arr2 = [1,3,5,7, undefined];
compareTwoArrays(arr1, arr2) // false

Array.every()

Another way of doing this comparison is by using the built-in every() method of array.

const compareTwoArrays = (a, b) => {
	// Write a guard clause to check the length of both arrays
	if (a.length !== b.length) return false;
	return a.every((elem, index) => elem === b[index])
}
let arr1 = [1,3,5,7];
let arr2 = [1,3,5,7];
compareTwoArrays(arr1, arr2) // true
let arr1 = [1,3,5,7, null];
let arr2 = [1,3,5,7, undefined];
compareTwoArrays(arr1, arr2) // false