'Does the .includes method in JavaScript loop through the array and case O(n)?

Does the .includes method cause O(n^2) when run with another loop such as in this simple example?

function myFn(){
    let age = people.map(person => {
            if(person > 21){
              return "YES";
        } else {
          return "NO";
        }
    return age.includes('NO') ? 'NO' : 'YES';
}
javascriptalgorithmloopsmethods


Solution 1:[1]

The method is specified such that it does indeed go through the array element by element. So that's O(n) (linear). But that's after your map, which has already gone all the way through the array.

JavaScript engine implementations are free (as always) to optimize provided optimizing doesn't change the semantics of the method.

As a side note, though, if you want to look through an array for an element matching an arbitrary condition, map+includes isn't your best choice; some and every are better, because they short-circuit (stop looping) when they find an element that passes (some) or fails (every) the test. Your code looks to see if every element in people is > 21, so that would be:

function myFn() {
    return people.every(person => person > 21) ? "YES" : "NO";
}

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