Generator = Object.getPrototypeOf(function* () {})

extend-generator.js

const Generator = Object.getPrototypeOf(function* () {});
Generator.prototype.takeWhile = function (pred) {
    const result = [];
    while (true) {
        const a = this.next();
        if (a.done || !pred(a.value)) break;
        result.push(a.value);
    }
    return result;
};

function* fib() {
    let [a, b] = [0, 1];
    while (true) {
        [a, b] = [a + b, a];
        yield a;
    }
}

console.log(fib().takeWhile(e => e < 100));