JavaScript Array: Checking for multiple values

We are required to write a JavaScript function that takes in two arrays of Numbers and checks whether all the elements of the first array exist in the second or not.

Example

The code for this will be ?

const arr1 = [34, 78, 89];
const arr2 = [78, 67, 34, 99, 56, 89];
const multipleIncludes = (first, second) => {
    const indexArray = first.map(el => {
        return second.indexOf(el);
    });
    return indexArray.indexOf(-1) === -1;
}
console.log(multipleIncludes(arr1, arr2));

Output

The output in the console ?

true

How It Works

The function maps each element from the first array to its index position in the second array using indexOf(). If an element doesn't exist, indexOf() returns -1. Finally, we check if any -1 exists in the index array.

Alternative Method: Using every()

A more readable approach uses the every() method:

const arr1 = [34, 78, 89];
const arr2 = [78, 67, 34, 99, 56, 89];

const multipleIncludes = (first, second) => {
    return first.every(element => second.includes(element));
}

console.log(multipleIncludes(arr1, arr2));
console.log(multipleIncludes([1, 2, 3], [2, 3, 4])); // false - 1 is missing

true
false

Comparison

Conclusion

Both methods work effectively for checking multiple values. The every() approach is more readable and potentially faster since it stops execution on the first missing element.