initLoading.js

const fs = require('fs');
function readImagesToArr() {
    return new Promise((res, rej) => {
        fs.readdir('images', 'utf8', (err, files) => {
            if (err) {
                console.log(err)
                throw err;
            }
            let filesArr = files;
            res(filesArr);
        })
    });
}
function addImagesDomToXml(filesArr) {
    return new Promise((res,rej)=>{
        fs.open('es2015/loading.ts', 'a+', (err, fd) => {
            if (err) {
                if (err.code === 'ENOENT') {
                    console.error('myfile does not exist');
                    return;
                }
                throw err;
            }
            let dom = 'new MyLoader([';
            for (let i = 0; i < filesArr.length; i++) {
                if(i===filesArr.length-1){
                    dom += '"images/' + filesArr[i] + '"'
                }else{
                    dom += '"images/' + filesArr[i] + '",'
                }
            }
            dom+='])';
            res({
                fd:fd,
                dom:dom
            });
        });
    })
}
function writeXML(fd,dom) {
    fs.write(fd, dom, 0, 'utf-8', (err, written, string) => {
        if (err) throw err;
        console.log('The file has been saved!');
    })
}
Promise
    .resolve()
    .then(()=>{
        return readImagesToArr()
    })
    .then((filesArr)=>{
        return addImagesDomToXml(filesArr)
    })
    .then((object)=>{
        writeXML(object.fd,object.dom)
    })