What's the difference between "new" and directly invoking a generator function?

Question

I know the difference between "new" and directly invoking a normal function.

But how about the case for the generator function?

e.g:

function *counter(){
    let n = 0;
    while (n < 2) {
        yield n++;
    }
    return 10;
}

var countIter1 = new counter();
var countIter2 = counter();

seems they're the same?

Answer 1

Generators allow you to define an iterative algorithm by writing a single function which can maintain its own state.A generator is a special type of function that works as a factory for iterators. A function becomes a generator if it contains one or more yield expressions.When a generator function is called the body of the function does not execute straight away; instead, it returns a generator-iterator object. Each call to the generator-iterator's next() method will execute the body of the function up to the next yield expression and return its result. When either the end of the function or a return statement is reached, a StopIteration exception is thrown. A generator function can be used directly as the iterator method of a class, greatly reducing the amount of code needed to create custom iterators.

 function Range(low, high){
      this.low = low;
      this.high = high;
    }
    Range.prototype.__iterator__ = function(){
      for (var i = this.low; i <= this.high; i++)
        yield i;
    };
    var range = new Range(3, 5);
    for (var i in range)
      print(i); // prints 3, then 4, then 5 in sequence

Not all generators terminate; it is possible to create a generator that represents an infinite sequence.