Funkcje generatorów, yield i małe potoki

Dlaczego generatory?

function* i yield

// A basic generator that yields 1..n lazily
function* countTo(n) {
  for (let i = 1; i <= n; i = i + 1) {
    yield i; // pause here and give i to the caller
  }
}

for (const x of countTo(3)) {
  console.log("value:", x);
}

Ręczne użycie next()

// You can also drive a generator manually with next()
const it = countTo(2);

console.log(it.next()); // { value: 1, done: false }
console.log(it.next()); // { value: 2, done: false }
console.log(it.next()); // { value: undefined, done: true }

Leniwe generowanie liczb parzystych

// Yield even numbers up to n (inclusive)
function* evensUpTo(n) {
  for (let i = 0; i <= n; i = i + 1) {
    if (i % 2 === 0) {
      yield i;
    }
  }
}

console.log("evens 0..6:", [...evensUpTo(6)]);

Leniwy potok mapowania

// map() as a generator: transform values lazily
function* map(iterable, fn) {
  for (const v of iterable) {
    yield fn(v);
  }
}

const doubled = map(countTo(4), function (x) { return x * 2; });
console.log("doubled:", [...doubled]);

Dobre praktyki

Quiz: wartość zwracana przez generator

Podsumowanie