| for await...of | 您所在的位置：网站首页 › 循环 await › for await...of |
|
for await...of 语句会在异步或者同步可迭代对象上创建一个迭代循环，包括 Set和自定义的异步或者同步可迭代对象。其会调用自定义迭代钩子，并为每个不同属性的值执行语句。 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. 语法 for await (variable of iterable) { statement } variable 在每次迭代中，将不同属性的值分配给变量。变量有可能以 const, let, 或者 var来声明。 iterable 被迭代枚举其属性的对象。 迭代异步可迭代对象你还可以迭代一个明确实现异步迭代协议的对象： var asyncIterable = { [Symbol.asyncIterator]() { return { i: 0, next() { if (this.i < 3) { return Promise.resolve({ value: this.i++, done: false }); } return Promise.resolve({ done: true }); } }; } }; (async function() { for await (num of asyncIterable) { console.log(num); } })(); // 0 // 1 // 2 迭代异步生成器异步生成器已经实现了异步迭代器协议, 所以可以用 for await...of循环。 async function* asyncGenerator() { var i = 0; while (i < 3) { yield i++; } } (async function() { for await (num of asyncGenerator()) { console.log(num); } })(); // 0 // 1 // 2有关使用for await... of考虑迭代API中获取数据的异步 generator 更具体的例子。这个例子首先为一个数据流创建了一个异步 generator，然后使用它来获得这个API的响应值的大小。 async function* streamAsyncIterator(stream) { const reader = stream.getReader(); try { while (true) { const { done, value } = await reader.read(); if (done) { return; } yield value; } } finally { reader.releaseLock(); } } // 从url获取数据并使用异步 generator 来计算响应值的大小 async function getResponseSize(url) { const response = await fetch(url); // Will hold the size of the response, in bytes. let responseSize = 0; // 使用for-await-of循环. 异步 generator 会遍历响应值的每一部分 for await (const chunk of streamAsyncIterator(response.body)) { // Incrementing the total response length. responseSize += chunk.length; } console.log(`Response Size: ${responseSize} bytes`); // expected output: "Response Size: 1071472" return responseSize; } getResponseSize('https://jsonplaceholder.typicode.com/photos'); 规范 Specification Status Comment ECMAScript Latest Draft (ECMA-262)ECMAScript Language: The for-in, for-of, and for-await-of Statements Draft ECMAScript 2018 (ECMA-262)ECMAScript Language: The for-in, for-of, and for-await-of Statements Standard 浏览器兼容 此页面上的兼容性表是根据结构化数据生成的。如果您想为数据做出贡献，请查看https://github.com/mdn/browser-compat-data并向我们发送拉取请求。 Update compatibility data on GitHub 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 for await...of Experimental Chrome Full support 63 Edge No support No Firefox Full support 57 IE No support No Opera Full support 50 Safari Full support 11 WebView Android Full support 63 Chrome Android Full support 63 Firefox Android Full support 57 Opera Android Full support 46 Safari iOS ? Samsung Internet Android Full support 8.0 nodejs Full support 10.0.0 Full support 10.0.0 No support 8.10.0 — 10.0.0 Disabled Disabled From version 8.10.0 until version 10.0.0 (exclusive): this feature is behind the --harmony-async-iteration runtime flag. Legend Full support Full support No support No support Compatibility unknown Compatibility unknown Experimental. Expect behavior to change in the future. Experimental. Expect behavior to change in the future. User must explicitly enable this feature. User must explicitly enable this feature. 相关链接 Statements/for...of |
| CopyRight 2018-2019 实验室设备网 版权所有 |