load( url, onLoad, onProgress, onError ) {

			const scope = this;
			const path = this.path === '' ? THREE.LoaderUtils.extractUrlBase( url ) : this.path;
			const loader = new THREE.FileLoader( this.manager );
			loader.setPath( this.path );
			loader.setRequestHeader( this.requestHeader );
			loader.setWithCredentials( this.withCredentials );
			loader.load( url, function ( text ) {

				try {

					onLoad( scope.parse( text, path ) );

				} catch ( e ) {

					if ( onError ) {

						onError( e );

					} else {

						console.error( e );

					}

					scope.manager.itemError( url );

				}

			}, onProgress, onError );

		}
Loads and parses a MTL asset from a URL.

@param {String} url - URL to the MTL file.
@param {Function} [onLoad] - Callback invoked with the loaded object.
@param {Function} [onProgress] - Callback for download progress.
@param {Function} [onError] - Callback for download errors.

@see setPath setResourcePath

@note In order for relative texture references to resolve correctly
you must call setResourcePath() explicitly prior to load.