Check out example codes for "ts generator". It will help you in understanding the concepts better.

Code Example 1

1) They only compute the next value when the user asks for it.(pause the 
    execution after every output) 
2) They can generate infinte values.
3) Calling a generator return in iterable iterator.

function* fibonacci(){
  let a = 0;
  let b = 1;
    yield a ;
    [a, b] = [b, a+b] ;
let f = fibonacci();
f().next()   // give 0
f().next()   // give 1

Learn ReactJs, React Native from