loader.js

import * as THREE from 'three';
import { EventEmitter } from 'events';

import 'three/examples/js/loaders/OBJLoader';

export default class MultipleOBJLoader extends EventEmitter {

  pathsToLoad = {};
  modelsLoaded = {};
  numLoaded = 0;

  constructor () {

    super();
  }

  registerPath (path, key) {
    
    if (!path) {

      throw new Error('required argument: path');
    }

    let _key;

    if (key) {
      _key = key;      
    } else {
      _key = path;
    }

    // already loaded
    if (this.modelsLoaded[_key]) {
      return;
    }

    this.pathsToLoad[_key] = path;
  }

  load () {
    
    const self = this;
    const numPaths = Object.keys(self.pathsToLoad).length;

    return new Promise(function (resolve, reject) {

      Object.keys(self.pathsToLoad).forEach(function (key) {

        (function (key) {

          var ldr = new THREE.OBJLoader();
          ldr.load(self.pathsToLoad[key], function (obj) {

            self.modelsLoaded[key] = obj;

            ++self.numLoaded;

            if (numPaths === self.numLoaded) {
              resolve(self.modelsLoaded);
            }
          }, function (xhr) {

            var parcent = xhr.loaded / xhr.total;
            var ratio = parcent / numPaths;
            self.emit('progress', ratio + ratio * self.numLoaded);
          });
        })(key);
      });
    });
  }

  getModelsLoaded () {

    return this.modelsLoaded;
  }
};