How to get the first item from an JavaScript iterator that satisfies a testing function

Question

I have an iterator object, and I would like to get the first element that satisfies a testing function.

I know I can use Array.prototype.find if I convert the iterator to an array. using the [...ducks].find((duck) => duck.age >= 3) syntax for example.

But I do not want to convert the iterator to an array because it's wasteful. In my example, I have many ducks, and I need an old one that will be found after only a few tests.

I'm wondering whether an elegant solution exists.

Answer 1

There's nothing built in, but you can readily write a function for it, stick it in your utilities toolkit, and reuse it:

function find(it, callback) {
    for (const value of it) {
        if (callback(value)) {
            return value;
        }
    }
}

Usage:

const duck = find(ducks, (duck) => duck.age >= 3);