generators.md

Generators

A generator is a special type of function in JavaScript that can pause its execution and then continue where it left off. It's defined with the function* syntax and uses the yield keyword to produce a sequence of values.

Key Concepts

• Generators return multiple values: Unlike regular functions, generators can return ("yield") multiple values one after another, on a per-request basis.
• Generator function: A generator function is defined with function* syntax.
• Yield: yield keyword is used in the generator function body to specify the values to be returned from the generator.
• next() method: After calling next() on a generator function, it returns an object with the properties value (the yielded value) and done (a boolean indicating whether the generator has yielded its last value).
• For..of: Generators can be used with the for..of loop to iterate over the yielded values. However, for..of won't return the last value when done is true. To fix this, we need to return all values using yield.
• yield*: It can delegate execution to another generator.
• Passing values with next(): We can send values back into the generator using the next(value) method. The value passed to next() is treated as the result of the last yield expression.
• Async generators: Async generators can be used for handling data that is loaded in chunks, allowing the asynchronous loading of additional data while the previous data is being processed.

Example

function* idGenerator() {
  let id = 0;
  while (true) {
    yield id++;
  }
}

const generator = idGenerator(); 

console.log(generator.next().value); // 0
console.log(generator.next().value); // 1
console.log(generator.next().value); // 2

In this example, idGenerator is an infinite generator that yields a new id each time its next method is called.