three.js/src/loaders/LoadingManager.js

/**
 * @author mrdoob / http://mrdoob.com/
 */

THREE.LoadingManager = function ( onLoad, onProgress, onError ) {

	var scope = this;

	var isLoading = false, itemsLoaded = 0, itemsTotal = 0;

	this.onLoad = onLoad;
	this.onProgress = onProgress;
	this.onError = onError;

	this.itemStart = function ( url ) {

		itemsTotal ++;

		if ( isLoading === false ) {

			if ( scope.onStart !== undefined ) {

				scope.onStart( url, itemsLoaded, itemsTotal );

			}

		}

		isLoading = true;

	};

	this.itemEnd = function ( url ) {

		itemsLoaded ++;

		if ( scope.onProgress !== undefined ) {

			scope.onProgress( url, itemsLoaded, itemsTotal );

		}

		if ( itemsLoaded === itemsTotal ) {

			isLoading = false;

			if ( scope.onLoad !== undefined ) {

				scope.onLoad();

			}

		}

	};

};

THREE.DefaultLoadingManager = new THREE.LoadingManager();