The existing MD files are as follows:
part1.md

part2.md

Fish encounter. Md

Demand: Read the contents of the above three files and output.

First, review how many files are implemented by reviewing how many files are implemented by using the THEN chain call call to promise?

code show as below:

// promise THEN chain call implementation
// introduce the FS module
const fs=require('fs');

const p=new Promise((resolve,reject)=>{
    fs.readFile('./part1.md',(err,data)=>{
        if(err){
            reject(err);
        }else{
            resolve(data);
        }
    });
});

p.then(function(value){
    return new Promise((resolve,reject)=>{
        fs.readFile('./part2.md',(err,data)=>{
            if(err){
                reject(err);
            }else{
                resolve([value,data]);
            }
        })
    })
}).then(function(value){
    return new Promise((resolve,reject)=>{
        fs.readFile('. / Fish encounter. Md',(err,data)=>{
            if(err){
                reject(err);
            }else{
                value.push(data);
                resolve(value);
            }
        })
    })
}).then(value=>console.log(value.join('\r\n')));

First of all, we must know that the THEN method is called, the result is the promise object, and the object status is determined by the return result of the callback function. The case is used here: If the callback function returns a successful promise object, then the return value of the THEN method is a promisesTatus for the promise object for success information, follow-up chain call.

Next, look at another method --ASYNC and AWAIT combine multiple files
code show as below:

// 1, introduce the FS module
const fs=require('fs');

// read part1.md
function readPart1(){
    return new Promise((resolve,reject)=>{
        fs.readFile('./part1.md',(err,data)=>{
            if(err){
                reject(err);
            }else{
                resolve(data);
            }
        })
    });
}

// Read part2.md
function readPart2(){
    return new Promise((resolve,reject)=>{
        fs.readFile('./part2.md',(err,data)=>{
            if(err){
                reject(err);
            }else{
                resolve(data);
            }
        })
    });
}

// read fish encounter. Md
function readMeet(){
    return new Promise((resolve,reject)=>{
        fs.readFile('. / Fish encounter. Md',(err,data)=>{
            if(err){
                reject(err);
            }else{
                resolve(data);
            }
        })
    });
}

// Await expression is placed in the Async function
// Declare an ASYNC function
async function readLyrics(){
    let part1=await readPart1();
    let part2=await readPart2();
    let meet=await readMeet();

    console.log(part1.toString());
    console.log(part2.toString());
    console.log(meet.toString());
}

readLyrics();

This method uses: "The value of the AWAIT P expression is the promisevalue value of the promise object P", so the async function is part1, part2, and meet is the result of reading three files, and then the output is line ~

Output results: