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• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

Symbol.asyncIterator well-known symbol specifies the default AsyncIterator for an object. If this property is set on an object, it is an async iterable and can be used in a for await...of loop.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

描述

Symbol.asyncIterator symbol is a builtin symbol that is used to access an object's @@asyncIterator method. In order for an object to be async iterable, it must have a Symbol.asyncIterator key.

特性属性在 Symbol.asyncIterator
可写	no
可枚举	no
可配置	no

范例

User-defined Async Iterables

You can define your own async iterable by setting the [Symbol.asyncIterator] property on an object.

const myAsyncIterable = {
    async* [Symbol.asyncIterator]() {
        yield "hello";
        yield "async";
        yield "iteration!";
    }
};
(async () => {
    for await (const x of myAsyncIterable) {
        console.log(x);
        // expected output:
        //    "hello"
        //    "async"
        //    "iteration!"
    }
})();
					

When creating an API, remember that async iterables are designed to represent something iterable — like a stream of data or a list —, not to completely replace callbacks and events in most situations.

Built-in Async Iterables

There are currently no built-in JavaScript objects that have the [Symbol.asyncIterator] key set by default. However, WHATWG Streams are set to be the first built-in object to be async iterable, with [Symbol.asyncIterator] recently landing in the spec.

规范

规范
ECMAScript (ECMA-262) The definition of 'Symbol.asyncIterator' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
asyncIterator	Chrome 63	Edge 79	Firefox 57	IE No	Opera 50	Safari 11.1	WebView Android 63	Chrome Android 63	Firefox Android No	Opera Android 46	Safari iOS No	Samsung Internet Android 8.0	nodejs 10.0.0

图例

完整支持

完整支持

不支持

不支持

另请参阅

• Iteration protocols
• for await... of

元数据

• 最后修改： Feb 19, 2020

相关话题

1. 标准内置对象
2. Symbol
3. 特性
   1. Symbol.asyncIterator
   2. Symbol.hasInstance
   3. Symbol.isConcatSpreadable
   4. Symbol.iterator
   5. Symbol.match
   6. Symbol.matchAll
   7. Symbol.prototype.description
   8. Symbol.replace
   9. Symbol.search
   10. Symbol.species
   11. Symbol.split
   12. Symbol.toPrimitive
   13. Symbol.toStringTag
   14. Symbol.unscopables
4. 方法
   1. Symbol.for()
   2. Symbol.keyFor()
   3. Symbol.prototype.toSource()
   4. Symbol.prototype.toString()
   5. Symbol.prototype.valueOf()
   6. Symbol.prototype[@@toPrimitive]
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()