Generator

Генератор - это объект, возвращаемый функцией-генератором и соответствующий как "Итерируемому" протоколу, так и протоколу "Итератор".

Синтаксис

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

var g = gen(); // "Generator { }"

Методы

Generator.prototype.next()

Возвращает значение, полученное выражением yield.

Generator.prototype.return()

Возвращает заданное значение и заканчивает генератор.

Generator.prototype.throw()

Выдает ошибку генератора.

Пример

Бесконечный Итератор

function* idMaker() {
    var index = 0;
    while(true)
        yield index++;
}

var gen = idMaker(); // "Generator { }"

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

Legacy generator objects

Firefox (SpiderMonkey) also implements an earlier version of generators in JavaScript 1.7, where the star (*) in the function declaration was not necessary (you just use the yield keyword in the function body). However, legacy generators are deprecated. Do not use them; they are going to be removed (баг 1083482).

Legacy generator methods

Generator.prototype.next()

Returns a value yielded by the yield expression. This corresponds to next() in the ES2015 generator object.

Generator.prototype.close()

Closes the generator, so that when calling next() an StopIteration error will be thrown. This corresponds to the return() method in the ES2015 generator object.

Generator.prototype.send()

Used to send a value to a generator. The value is returned from the yield expression, and returns a value yielded by the next yield expression. send(x) corresponds to next(x) in the ES2015 generator object.

Generator.prototype.throw()

Throws an error to a generator. This corresponds to the throw() method in the ES2015 generator object.

Legacy generator example

function fibonacci() {
  var a = yield 1;
  yield a * 2;
}

var it = fibonacci();
console.log(it);          // "Generator {  }"
console.log(it.next());   // 1
console.log(it.send(10)); // 20
console.log(it.close());  // undefined
console.log(it.next());   // throws StopIteration (as the generator is now closed)

Specifications

Browser compatibility

See also

Legacy generators

• The legacy generator function
• The legacy generator function expression
• StopIteration
• The legacy Iterator protocol

ES2015 generators

• Functions
• function
• function expression
• Function
• function*
• function* expression
• GeneratorFunction
• The Iterator protocol