ById( 'pos' );
			var moveBtn = document.getElementById( 'moveBtn' );
			var cancelBtn = document.getElementById( 'cancelBtn' );
			var MoveCommand = function( receiver, pos ){
				this.receiver = receiver;
				this.pos = pos;
				this.oldPos = null;
			};
			MoveCommand.prototype.execute = function(){
				this.receiver.start( 'left', this.pos, 1000, 'strongEaseOut' );
				this.oldPos = this.receiver.dom.getBoundingClientRect()[ this.receiver.propertyName ];
					// 记录小球开始移动前的