infinite-fibonacci-generator.js

function * fibonacciGen() {
  let prev1 = 1;
  let prev2 = 1;
  while (true) {
    let next = prev1 + prev2;
    yield prev1;
    prev1 = prev2;
    prev2 = next;
  }
}

const fib = fibonacciGen();

// print first 10 fibonacci numbers
for (let i = 0; i < 10; i++) {
  console.log(fib.next().value)  // 1 1 2 3 5 8 13 21 34 55
}

// since generators  return an Interator
// we can also use for..of on them
// here's another way to print the same result
let limit = 10;
for (const num of fibonacciGen()) {
  if (limit === 0) {
    break;
  }
  console.log(num); // 1 1 2 3 5 8 13 21 34 55
  limit = limit - 1;
}