Javascript Generators and Iterators

jsGenerators.js

// Iterators
const alpha = ['a','b','c'];
const it = alpha[Symbol.iterator]();
 
it.next();  //{ value: 'a', done: false }
it.next();  //{ value: 'b', done: false }
it.next();  //{ value: 'c', done: false }
it.next();  //{ value: undefined, done: true }

// Generate Fibonacci Sequence using Generator Function

function *fibGen() {
    let current = 0;
    let next = 1;
     
    while(true) {
        yield current;
        let nextNum = current + next;
        current = next;
        next = nextNum;
    }
}
 
let it = fibGen();
 
it.next().value;    //0
it.next().value;    //1
it.next().value;    //1
it.next().value;    //2

// Generator function

function* foo() {
  yield 'a';
  yield 'b';
  yield 'c';
}

for (const val of foo()) {
  console.log(val);
}
// a
// b
// c

const [...values] = foo();
console.log(values); // ['a','b','c']

// Communication with Generators

function* crossBridge() {
  const reply = yield 'What is your favorite color?';
  console.log(reply);
  if (reply !== 'yellow') return 'Wrong!'
  return 'You may pass.';
}

{
  const iter = crossBridge();
  const q = iter.next().value; // Iterator yields question
  console.log(q);
  const a = iter.next('blue').value; // Pass reply back into generator
  console.log(a);
}

// What is your favorite color?
// blue
// Wrong!


{
  const iter = crossBridge();
  const q = iter.next().value;
  console.log(q);
  const a = iter.next('yellow').value;
  console.log(a);
}

// What is your favorite color?
// yellow
// You may pass.

// Generators + Promises