javascript - Async/Await报错

问题描述

这段代码问题在哪，一运行就报错

var sleep = async function(para) {return new Promise(function(resolve, reject) { setTimeout(function() {resolve(para * para) }, 1000)}) } var errorSleep =async function(para) {return new Promise(function(resolve, reject) { setTimeout(function() {reject(’ ErrorSleep’) }, 1000)}) } try {var result1 = await sleep(1);var result2 = await errorSleep(4);var result3 = await sleep(1);console.log(’result1: ’, result1)console.log(’result2: ’, result2)console.log(’result3: ’, result3) } catch (err) {console.log(’err: ’, err)console.log(’result1: ’, result1)console.log(’result2: ’, result2)console.log(’result3: ’, result3) }

问题解答

await 只能在 async 包装的函数里面用。就和yield只能在generator函数里面用一样。

楼上不是说了吗，丢到async函数里。

var sleep = async function(para) {return new Promise(function(resolve, reject) { setTimeout(function() {resolve(para * para) }, 1000)}) } var errorSleep =async function(para) {return new Promise(function(resolve, reject) { setTimeout(function() {reject(’ ErrorSleep’) }, 1000)}) }//一样丢到async函数里 var af = async function() {try { var result1 = await sleep(1); var result2 = await errorSleep(4); var result3 = await sleep(1); console.log(’result1: ’, result1) console.log(’result2: ’, result2) console.log(’result3: ’, result3)} catch (err) { console.log(’err: ’, err) console.log(’result1: ’, result1) console.log(’result2: ’, result2) console.log(’result3: ’, result3)} } af();回答3：

await 只能在 async 函数(函数，函数表达式，箭头函数) 中使用，所以你只需要写个 async 函数把那段代码包起来就好了，我比较喜欢写 main 函数而不是直接在全局作用域内运行

async function main() { try {var result1 = await sleep(1);var result2 = await errorSleep(4);var result3 = await sleep(1);console.log('result1: ', result1);console.log('result2: ', result2);console.log('result3: ', result3); } catch (err) {console.log('err: ', err);console.log('result1: ', result1);console.log('result2: ', result2);console.log('result3: ', result3); }}// 记得调用main();

另外也可以使用 async IIFE 表达式，比如

// IIFE 函数表达式(async function() { // todo main process})();// IIFE Lambda 表达式(箭头函数表达式)(async () => { // todo main process})();