Symbol.iterator

¥Value

众所周知的符号 Symbol.iterator。

¥The well-known symbol Symbol.iterator.

¥Description

每当一个对象需要迭代时（例如在 for...of 循环开始时），就会不带参数地调用其 [Symbol.iterator]() 方法，并使用返回的迭代器来获取要迭代的值。

¥Whenever an object needs to be iterated (such as at the beginning of a for...of loop), its [Symbol.iterator]() method is called with no arguments, and the returned iterator is used to obtain the values to be iterated.

某些内置类型具有默认迭代行为，而其他类型（例如 Object）则没有。一些具有 [Symbol.iterator]() 方法的内置类型是：

¥Some built-in types have a default iteration behavior, while other types (such as Object) do not. Some built-in types with a [Symbol.iterator]() method are:

• Array.prototype[Symbol.iterator]()
• TypedArray.prototype[Symbol.iterator]()
• String.prototype[Symbol.iterator]()
• Map.prototype[Symbol.iterator]()
• Set.prototype[Symbol.iterator]()

另请参阅 迭代协议 了解更多信息。

¥See also Iteration protocols for more information.

¥Examples

¥User-defined iterables

我们可以像这样创建自己的迭代：

¥We can make our own iterables like this:

const myIterable = {};
myIterable[Symbol.iterator] = function* () {
  yield 1;
  yield 2;
  yield 3;
};
[...myIterable]; // [1, 2, 3]

或者可以使用 计算属性 直接在类或对象内部定义迭代：

¥Or iterables can be defined directly inside a class or object using a computed property:

class Foo {
  *[Symbol.iterator]() {
    yield 1;
    yield 2;
    yield 3;
  }
}

const someObj = {
  *[Symbol.iterator]() {
    yield "a";
    yield "b";
  },
};

console.log(...new Foo()); // 1, 2, 3
console.log(...someObj); // 'a', 'b'

¥Non-well-formed iterables

如果可迭代对象的 [Symbol.iterator]() 方法不返回迭代器对象，则它是非格式良好的可迭代对象。像这样使用它可能会导致运行时异常或错误行为：

¥If an iterable's [Symbol.iterator]() method does not return an iterator object, then it is a non-well-formed iterable. Using it as such is likely to result in runtime exceptions or buggy behavior:

const nonWellFormedIterable = {};
nonWellFormedIterable[Symbol.iterator] = () => 1;
[...nonWellFormedIterable]; // TypeError: [Symbol.iterator]() returned a non-object value

¥See also

• core-js 中 Symbol.iterator 的 Polyfill
• 迭代协议
• Array.prototype[Symbol.iterator]()
• TypedArray.prototype[Symbol.iterator]()
• String.prototype[Symbol.iterator]()
• Map.prototype[Symbol.iterator]()
• Set.prototype[Symbol.iterator]()
• arguments[Symbol.iterator]()
• Segments.prototype[Symbol.iterator]()