fibonacci.generator.js

function *fibonocci(t) {
  let a = 1, b = 0, c = 0;
  while(c < t) {
    yield c;
    c = a + b;
    a = b; b = c;
  }
}

let output = Array.from(fibonocci(21), n => n * 2);
console.log(output);