index.js

#!/usr/bin/env node

var fs = require("fs");

function printUsage(code) {
   console.log(`Usage: ${__filename} [-h] <asset_folder> <output_file>`);
   console.log('  asset_folder: The folder containing the source assets for the module being created.');
   console.log('  output_file:  The resulting javascript source file where the module will be written. This file can be required after running pre-require to load the source assets.');
   process.exit(code || 0);
 }

const args = process.argv.slice(2);
const env = process.env.NODE_ENV;

if (env !== 'test') {
  if (args.length === 1 && (args[0] === '-h')) {
    printUsage();
  }

  if (args.length !== 2) {
    console.log('Error: required command line arguments not provided.');
    printUsage(1);
  }

  const FOLDER_PATH = (args[0][0] == "./")?args[0]:"./"+args[0];
  const MODULE_NAME = args[1];

  loopDirectory (FOLDER_PATH, {}).then((val)=> {
      let assetsFileContent = `
// import this file for static assets
let Obj = {
  ${JSON.stringify(val).substr(1).slice(0, -1).replace(new RegExp('"', 'g'),'')},
  search: ${searchFile},
  format: ${searchFileFormat}
}
export default Obj;
      `;
      fs.writeFile (MODULE_NAME, assetsFileContent, function(err) {
          if (err) throw err;
          console.log('Pre-require');
          console.log('===========');
          console.log('Created module for required assets from ', FOLDER_PATH);
          console.log('Output file is: ' + MODULE_NAME);
      });
  });
}

export const searchFile = function(key) {
  if(this.hasOwnProperty(key)) {
    return this[key];
  } else {
    return -1;
  }
}

export const searchFileFormat = function(extension) {
  let filteredArray = this.filter(assetSlug => (assetSlug.includes("-"+extention)));
  if(filteredArray.length){
    return filteredArray;
  } else {
    return -1;
  }
}

export const loopDirectory = (path, obj) => {
    let directoryToRead = [];
    return new Promise((resolve) => {
         fs.readdir(path, function(err, items) {
             items.forEach((file) => {
                 let prePath = (path[path.length - 1] == "/")?path:path+"/";
                 let stats = fs.lstatSync(prePath + file);
                 let normalizeFileName = file.replace('.', '_').replace(/-/g, '_');
                 if (stats.isDirectory()) {
                     obj[normalizeFileName] = {};
                     //push it to the array so that we can loop and perform recursion based on that folder
                     directoryToRead.push({
                        normalizeFileName,
                        path: prePath + file
                     });
                 } else {
                     obj[normalizeFileName] = `require('${prePath + file}')`;
                 }
             });

             if (directoryToRead.length === 0) {
                 // if no more directory to read then we resolve it
                 resolve(obj);
             } else {
                 // if let say more than 1 directory inside the
                 // folder then we need to resolve when everything have been resolved
                 let promises = directoryToRead.map(val => {
                     return loopDirectory(val.path, obj[val.normalizeFileName])
                 });
                 Promise.all(promises).then(()=> {
                     resolve(obj);
                 });
             }
         });
     });
 };