Fibonacci generator: https://jsfiddle.net/remarkablemark/592n8ub7/

fibonacci-generator.js

/**
 * Fibonacci sequence generator.
 * https://developer.mozilla.org/docs/Web/JavaScript/Guide/Iterators_and_Generators#Advanced_generators
 *
 * @return {Number}
 */
function* fibonacci() {
  let [a, b] = [0, 1];
  let current;
  while (true) {  
    yield current = a;
    a = b;
    b += current;
  }
}

// test
const fib = fibonacci();
Array(10).fill().forEach(_ => console.log(fib.next().value));