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javascript - Async/Await报错

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)
    }
    
    

高洛峰高洛峰2703 天前889

全部回复(3)我来回复

  • 三叔

    三叔2017-06-17 09:17:45

    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。

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    0
  • 为情所困

    为情所困2017-06-17 09:17:45

    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();

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    0
  • 黄舟

    黄舟2017-06-17 09:17:45

    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
    })();

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    0
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