在此页

• 句法
• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

AsyncFunction 构造函数 creates a new async function object. In JavaScript, every asynchronous function is actually an AsyncFunction 对象。

注意， AsyncFunction is not a global object. It can be obtained with the following code:

Object.getPrototypeOf(async function(){}).constructor
					

句法

new AsyncFunction([arg1[, arg2[, ...argN]],] functionBody)
					

参数

arg1, arg2, ... arg N

Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example " x ", " theValue ", or " a,b ".

functionBody

A string containing the JavaScript statements comprising the function definition.

描述

async function objects created with the AsyncFunction constructor are parsed when the function is created. This is less efficient than declaring an async function with an 异步函数表达式 and calling it within your code, because such functions are parsed with the rest of the code.

All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed.

注意： async functions created with the AsyncFunction constructor do not create closures to their creation contexts; they are always created in the global scope.

When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the AsyncFunction constructor was called.

This is different from using eval with code for an async function expression.

援引 AsyncFunction 构造函数作为函数 (不使用 new 运算符) 有相同效果若把它作为构造函数进行援引。

范例

Creating an async function from an AsyncFunction() constructor

function resolveAfter2Seconds(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(x);
    }, 2000);
  });
}
let AsyncFunction = Object.getPrototypeOf(async function(){}).constructor
let a = new AsyncFunction('a',
                          'b',
                          'return await resolveAfter2Seconds(a) + await resolveAfter2Seconds(b);');
a(10, 20).then(v => {
  console.log(v); // prints 30 after 4 seconds
});
					

规范

规范
ECMAScript (ECMA-262) The definition of 'AsyncFunction object' 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
AsyncFunction	Chrome 55	Edge 15	Firefox 52	IE No	Opera 42	Safari 10.1	WebView Android 55	Chrome Android 55	Firefox Android 52	Opera Android 42	Safari iOS 10.3	Samsung Internet Android 6.0	nodejs 7.6.0 7.6.0 7.0.0 Disabled Disabled From version 7.0.0: this feature is behind the --harmony runtime flag.

图例

完整支持

完整支持

不支持

不支持

用户必须明确启用此特征。

用户必须明确启用此特征。

另请参阅

• async function function
• 异步函数表达式
• Function
• function statement
• 函数表达式
• 函数和函数作用域

元数据

• 最后修改： May 13, 2020

相关话题

1. 标准内置对象
2. AsyncFunction
3. 继承：
4. Function
5. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
6. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
7. Object
8. 特性
   1. Object.prototype.__proto__
   2. Object.prototype.constructor
9. 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()