Basic of async.

async.js

 const fs = require('fs')

function myReaddir() {
	return new Promise((resolve, reject) => { 
		fs.readdir("./aaa", function(err, files){
			if(err) {
				reject(err);
			} else {
				resolve(files);
			}	
		})

	})
}

function myReadFile(file) {
	console.log("....", file);
	return new Promise((resolve, reject) => {
		fs.readFile("./aaa/" + file, function(err, data) {
			if(err) reject(err);
			else resolve(data);
		})
	})
}


//myReaddir().then((data)=> {
//	myReadFile(data[0]).then((content)=>{
//		console.log("content:", content.toString());
//	})
//}).catch((err) => {
//	console.log(">>>", err);
//});
async function readFiles() {

	let files;
	try {
 		files = await myReaddir();
	} catch(err) {
 		console.log("Error:", err);
	}
	console.log(">>>", files);
	
	let fileContent;
	try {
		fileContent = await myReadFile(files[0]);
	} catch(err) {
	 	throw err;
	}

	console.log("File content:", fileContent.toString());
}

readFiles();