Question

我有一个代码，等待文件存在并返回文件内容。我运行代码，它等待'smscode.txt'文件。我上传“ smscode.txt”代码后，执行完成。没错。

但是出于某种原因console.log（2）;什么都不显示。这是我执行函数的结果。

c:\work\docker\test-npm>node ideaOpen.js
1

c:\work\docker\test-npm>

更新和简化的代码版本，没有文件

我希望显示“ 2”，但不会显示。在5秒钟内脚本成功完成了工作。

let smsCode = '';
function checkSmsCode() {
    setTimeout(function(){
        smsCode = 1234;
    }, 5000);
}
checkSmsCode();

let smsCodeExist = new Promise((resolve, reject) => {
    if (smsCode) {
        resolve(smsCode);
    }
});

(async () => {
    console.log(1);
    let a = await smsCodeExist;
    console.log(2);
})();

Answer 1

借助这个stackoverflow问题，我找到了一个解决方案。 Use Promise to wait until polled condition is satisfied

let smsCode = '';
function checkSmsCode() {
    setTimeout(function(){
        smsCode = 1234;
    }, 5000);
}
checkSmsCode();

let smsCodeExist = new Promise(function (resolve, reject) {
    waitForSmsCode(resolve);
});


function waitForSmsCode(resolve) {
    if (!smsCode) {
        setTimeout(waitForSmsCode.bind(this, resolve), 500);
    } else {
        resolve(smsCode);
    }
}

(async () => {
    console.log(1);
    let a = await smsCodeExist;
    console.log(2);
    console.log(a);
})();

P.S。读取文件时回答原始问题（脚本等到文件存在）


    var fs = require('fs');
    let smsCode = '';

    function waitForSmsCode(resolve) {
        fs.readFile('smscode.txt', 'utf8', (err, contents) => {
            smsCode = contents;
        });
        if (!smsCode) {
            setTimeout(waitForSmsCode.bind(this, resolve), 500);
        } else {
            resolve(smsCode);
        }
    }

    let smsCodeExist = new Promise((resolve, reject) => {
        waitForSmsCode(resolve);
    });

    (async () => {
        console.log(1);
        let smsCode = await smsCodeExist;
        console.log(smsCode);
    })();

在等待之后console.log不会返回异步结果

1 个答案: