Functions That Can Be Paused

Generators are a special kind of function that can pause their execution midway, yield a value, and then resume from exactly where they left off. They are declared with an asterisk: function*.

Basic Syntax

function* generateSequence() {
  console.log('Starting...');
  yield 1;              // Pause and return 1
  console.log('Resumed!');
  yield 2;              // Pause and return 2
  return 'Finished';   // Done!
}

const gen = generateSequence();
console.log(gen.next()); // { value: 1, done: false }  -- "Starting..." logs
console.log(gen.next()); // { value: 2, done: false }  -- "Resumed!" logs
console.log(gen.next()); // { value: 'Finished', done: true }

Generators Are Iterable

You can use them with for...of:

for (let value of generateSequence()) {
  console.log(value); // logs: 1, then 2  (does NOT include the return value)
}

Why Use Generators?

1. Custom iterators: Build your own iterable objects cleanly.
2. Memory efficiency: Generate values on demand without creating a huge array in memory.
3. Infinite sequences: Represent things like " all natural numbers " without pre-computing them.