Javascript 将异步转换为Promise

我建议，您不应该直接从其他函数调用回调函数.相反，让函数保持简单并返回输出即可.创建一个父函数，使用关键字await逐行调用所有函数，并传递输出.请参阅以下代码:

const chalk = require('chalk');
const ProgressBar = require('progress');
const fs = require('fs');
const path = require('path');
async function* walk(dir) {
    for await (const d of await fs.promises.opendir(dir)) {
        const entry = path.join(dir, d.name);
        if (d.isDirectory()) yield* await walk(entry);
        else if (d.isFile()) yield entry;
    }
}

async function scan() {
    var docs = [];
    for await (const p of walk('docs')) {
        if (p.endsWith('.md')) {
            console.log(p);
            docs.push(p);
        }
    }
    docs.sort();
    return docs;
}

async function inspect(docs) {
    const bar = new ProgressBar(':bar', { total: docs.length });
    for (f in docs) {
        if (bar.curr === 0) {
            console.log(chalk.green('starting...'));       
        }
        bar.tick();
        // do other work and (possibly) modify `docs` array
        if (bar.complete) {
            console.log(chalk.green('done.'));
        }
    }
    // pass docs to next stage
    return docs;
}

async function nextStage(docs){
    // do some stuff and return something
}

async function main(){
    try {
        let docs = await scan();
        docs = await inspect(docs);
        let nextValue = await nextStage(docs);
        // keep adding the calls here. It is more maintainable
    } catch(e){
        // handle the exception here 
    }
}

编辑:要使用Promise执行此操作，您可以参考以下代码.它不是代码的直接转换，但我希望它简化了事情，并且您可以理解如何使用promise :

async function* walk(dir) {
    let files = ['A.txt', 'B.txt', 'A.md', 'B.md', 'c.md'];
    for(file of files){
        yield file;
    }
}

async function scan() {
    var docs = [];
    for await (const p of walk('docs')) {
        if (p.endsWith('.md')) {
            console.log(p);
            docs.push(p);
        }
    }
    docs.sort();
    // return a promise here 
    return new Promise(function (resolve, reject) {
        // Pass the arguments in resolve() 
        resolve(docs);
        // you can also call reject(error) to invoke the catch method
    })
}

async function inspect(docs) {
    // here I am simply renaming the files 
    for(let i=0; i<docs.length; ++i){
        docs[i] = "Renamed"+docs[i];
    }
    console.log("Renamed successfully");
    return docs;
}

async function nextStage(docs){
    // do some stuff and return something
    // lets print the files simply 
    console.log(docs);
    // and return anything if needed 
    return docs.length;
}

scan()
    .then(inspect)
    .then(nextStage)
    .catch((error)=>{
        // handle the error here 
    });

只需注意我们如何从第一个函数返回Promise对象.我们将数据传递给Resolve()，它将作为参数注入到.then()调用中提到的下一个函数中.无论您在哪里抛出任何错误或调用Reject()函数，您都可以跳到.catch()调用.请注意，每个链接的调用都返回一个Promise对象，以便您可以进一步链接它(在调试器中运行它以查看您自己).