load( url, onLoad, onProgress, onError ) {

		const loader = new FileLoader( this.manager );
		loader.setPath( this.path );
		loader.setRequestHeader( this.requestHeader );
		loader.setWithCredentials( this.withCredentials );
		loader.load( url, ( text ) => {

			try {

				onLoad( this.parse( JSON.parse( text ) ) );

			} catch ( e ) {

				if ( onError ) {

					onError( e );

				} else {

					console.error( e );

				}

				this.manager.itemError( url );

			}

		}, onProgress, onError );

	}
Loads the node definitions from the given URL.

@param {string} url - The path/URL of the file to be loaded.
@param {Function} onLoad - Will be called when load completes.
@param {Function} onProgress - Will be called while load progresses.
@param {Function} onError - Will be called when errors are thrown during the loading process.