What are generator functions and how do they work?

Generator functions are special functions that can pause execution and resume later, allowing them to produce a sequence of values over time instead of computing them all at once.

     function* numberGenerator() {
       yield 1;
       yield 2;
       yield 3;
     }

     const gen = numberGenerator();
     console.log(gen.next()); // { value: 1, done: false }
     console.log(gen.next()); // { value: 2, done: false }
     console.log(gen.next()); // { value: 3, done: false }
     console.log(gen.next()); // { value: undefined, done: true }
     

Key features:

1. Lazy evaluation:

        function* infiniteSequence() {
          let i = 0;
          while (true) {
            yield i++;
          }
        }
        

1. Two-way communication:

        function* twoWay() {
          const x = yield 'First';
          yield `Got: ${x}`;
        }

        const gen = twoWay();
        console.log(gen.next());      // { value: 'First', done: false }
        console.log(gen.next('data')); // { value: 'Got: data', done: false }
        

1. Delegating to other generators:

        function* gen1() { yield 1; yield 2; }
        function* gen2() {
          yield* gen1();
          yield 3;
        }
        

Practical uses: iterating large datasets, implementing custom iterators, managing async flows (though async/await is now preferred).