問題描述

這段代碼問題在哪，一運行就報錯

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) }

問題解答

await 只能在 async 包裝的函數里面用。就和yield只能在generator函數里面用一樣。

樓上不是說了嗎，丟到async函數里。

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)}) }//一樣丟到async函數里 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 函數(函數，函數表達式，箭頭函數) 中使用，所以你只需要寫個 async 函數把那段代碼包起來就好了，我比較喜歡寫 main 函數而不是直接在全局作用域內運行

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); }}// 記得調用main();

另外也可以使用 async IIFE 表達式，比如

// IIFE 函數表達式(async function() { // todo main process})();// IIFE Lambda 表達式(箭頭函數表達式)(async () => { // todo main process})();