生成器

Generator 对象由 generator function 返回,它符合 可迭代协议迭代器协议

¥The Generator object is returned by a generator function and it conforms to both the iterable protocol and the iterator protocol.

Generator 是隐藏 Iterator 类的子类。

¥Generator is a subclass of the hidden Iterator class.

Try it

构造函数

¥Constructor

没有与 Generator 构造函数相对应的 JavaScript 实体。Generator 的实例必须从 生成器函数 返回:

¥There's no JavaScript entity that corresponds to the Generator constructor. Instances of Generator must be returned from generator functions:

js
function* generator() {
  yield 1;
  yield 2;
  yield 3;
}

const gen = generator(); // "Generator { }"

console.log(gen.next().value); // 1
console.log(gen.next().value); // 2
console.log(gen.next().value); // 3

只有一个隐藏对象,它是由生成器函数创建的所有对象共享的原型对象。该对象通常被风格化为 Generator.prototype,使其看起来像一个类,但它应该更合适地称为 GeneratorFunction.prototype.prototype,因为 GeneratorFunction 是一个实际的 JavaScript 实体。要了解 Generator 实例的原型链,请参阅 GeneratorFunction.prototype.prototype

¥There's only a hidden object which is the prototype object shared by all objects created by generator functions. This object is often stylized as Generator.prototype to make it look like a class, but it should be more appropriately called GeneratorFunction.prototype.prototype, because GeneratorFunction is an actual JavaScript entity. To understand the prototype chain of Generator instances, see GeneratorFunction.prototype.prototype.

实例属性

¥Instance properties

这些属性在 Generator.prototype 上定义并由所有 Generator 实例共享。

¥These properties are defined on Generator.prototype and shared by all Generator instances.

Generator.prototype.constructor

创建实例对象的构造函数。对于 Generator 实例,初始值为 GeneratorFunction.prototype

注意:Generator 对象不存储对创建它们的生成器函数的引用。

¥Note: Generator objects do not store a reference to the generator function that created them.

Generator.prototype[Symbol.toStringTag]

[Symbol.toStringTag] 属性的初始值为字符串 "Generator"。该属性在 Object.prototype.toString() 中使用。

实例方法

¥Instance methods

还从其父级 Iterator 继承实例方法。

¥Also inherits instance methods from its parent Iterator.

Generator.prototype.next()

返回 yield 表达式产生的值。

Generator.prototype.return()

就像在当前暂停位置将 return 语句插入到生成器主体中一样,该语句完成生成器并允许生成器在与 try...finally 块组合时执行任何清理任务。

Generator.prototype.throw()

就像在生成器主体的当前挂起位置插入一条 throw 语句一样,它通知生成器错误情况并允许其处理错误,或者执行清理并自行关闭。

示例

¥Examples

无限迭代器

¥An infinite iterator

使用生成器函数,直到需要时才会评估值。因此,生成器允许我们定义潜在无限的数据结构。

¥With a generator function, values are not evaluated until they are needed. Therefore a generator allows us to define a potentially infinite data structure.

js
function* infinite() {
  let index = 0;

  while (true) {
    yield index++;
  }
}

const generator = infinite(); // "Generator { }"

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

规范

Specification
ECMAScript Language Specification
# sec-generator-objects

¥Specifications

浏览器兼容性

BCD tables only load in the browser

¥Browser compatibility

也可以看看