var fs = require('fs');var a = new Promise(function(resolve, reject) {    fs.readFile('./1.txt', 'utf-8', function(err, data) {        if (err) {            return reject(err);        }        resolve(data);    });});var b = new Promise(function(resolve, reject) {    fs.readFile('./2.txt', 'utf-8', function(err, data) {        if (err) {            return reject(err);        }        resolve(data);    });});a.then(function(res1) {    console.log('res1');    console.log(res1);    b.then(function(res2) {        console.log('res1 + res2');        console.log(res1 + res2);    });});// b.then(function(result){
    //     console.log(result);// });fs.readFile('./1.txt', 'utf-8', function(err, data1) {    if (err) {        return reject(err);    } else {        console.log('data1');        console.log(data1);        fs.readFile('./2.txt', 'utf-8', function(err, data2) {            if (err) {                return reject(err);            } else {                console.log('data1 + data2');                console.log(data1 + data2);            }        });    }});