What are JavaScript Generators?

[mharoot]

source

https://codeburst.io/what-are-javascript-generators-and-how-to-use-them-c6f2713fd12e

(function start(){

  function makeRangeIterator(start = 0, end = Infinity, step = 1) {
      let nextIndex = start;
      let iterationCount = 0;

      const rangeIterator = {
         next: function() {
             let result;
             if (nextIndex < end) {
                 result = { value: nextIndex, done: false }
                 nextIndex += step;
                 iterationCount++;
                 return result;
             }
             return { value: iterationCount, done: true }
         }
      };
      return rangeIterator;
  }
  function runMakeRangeIteratorTest() {
    let it = makeRangeIterator(1, 10, 2);

    let result = it.next();
    while (!result.done) {
     console.log(result.value); // 1 3 5 7 9
     result = it.next();
    }

    console.log("Iterated over sequence of size: ", result.value); // 5
  }
  
function * generatorForLoop(num) {
  for (let i = 0; i < num; i += 1) {
    yield console.log(i);
  }
}

const genForLoop = generatorForLoop(5);

genForLoop.next(); // first console.log - 0
genForLoop.next(); // 1
genForLoop.next(); // 2
genForLoop.next(); // 3
genForLoop.next(); // 4

})();

[mharoot]

Prime Number Generator

(function start(){
  function isPrime(num) {
    for ( var i = 2; i < num; i++ ) {
      if ( num % i === 0 ) {
        return false;
      }
    }
    return true;
  }
  function* primeNumGenerator( start = 2, stop = 100 ) {
    for ( var i = start; i < stop; i++) {
      if ( isPrime(i) ) yield i;
      else continue;
    }
  }

  let it = primeNumGenerator(2, 100);
  alert( it.next().value );
  alert( it.next().value );
  alert( it.next().value );
  alert( it.next().value );
})();