How to check whether multiple values exist within a JavaScript array

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.

Following are our arrays ?

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

Let's write the code and check for multiple values ?

Using indexOf() Method

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

const contains = (first, second) => {
    const indexArray = first.map(el => {
        return second.indexOf(el);
    });
    return indexArray.indexOf(-1) === -1;
}

console.log(contains(arr1, arr2));

true

Using every() Method (Recommended)

A more elegant approach uses the every() method to check if all elements exist:

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

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

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

true
false

Using Set for Better Performance

For larger arrays, converting the second array to a Set improves lookup performance:

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

const containsAllOptimized = (first, second) => {
    const set = new Set(second);
    return first.every(element => set.has(element));
}

console.log(containsAllOptimized(arr1, arr2));

true

Comparison

Conclusion

Use every() with includes() for readable code, or combine with Set for better performance with large arrays. The every() method provides the most intuitive approach to check if all elements exist.