JavaScript generators are a special type of function that can be paused and resumed, allowing you to control the flow of execution and produce a series of values. This makes them a powerful tool for tasks such as iterating through a large dataset or generating a stream of data.

To define a generator function, you use the function* syntax instead of the regular function keyword. Inside the generator, you can use the yield keyword to pause the function and produce a value. When the generator is resumed, it picks up right where it left off, allowing you to iterate through a series of values without the need for a loop.

Here is an example of a simple generator that produces the Fibonacci sequence:

function* fibonacci() {
  let [prev, curr] = [0, 1];
  while (true) {
    yield curr;
    [prev, curr] = [curr, prev + curr];
  }
}

const sequence = fibonacci();
console.log(sequence.next().value); // 1
console.log(sequence.next().value); // 1
console.log(sequence.next().value); // 2
console.log(sequence.next().value); // 3
console.log(sequence.next().value); // 5

You can use the next() method to advance the generator to the next value. The method returns an object with a value property that contains the yielded value, and a done property that is true when the generator has completed.

Generators can also be used in combination with the for-of loop, which allows you to iterate through a series of values without the need for a traditional loop.

for (let value of fibonacci()) {
  console.log(value);
  if (value > 100) {
    break;
  }
}

In addition, you can use the yield* statement inside a generator to delegate to another generator or iterable object. This allows you to easily compose multiple generators together and create more complex data streams.

Generators are a powerful feature in JavaScript that can help you write more elegant and efficient code. They allow you to control the flow of execution, iterate through a series of values, and create complex data streams. With their help, you can easily create efficient, sophisticated, and robust applications.

Thanks for reading, happy hacking!

Originally posted in my personal blog: https://blog.luispa.dev/posts/mastering-javascript-generators-understanding-and-using-the-power-of-pausable-functions