extjs如何操作panel中的html属性,既改变html的值

panelhtml.js

{
  					title : "Variable",
						id : "Variable",
						region : "center",
						layout : "border",
						bodyStyle : 'background-color:#FFFFFF',// 设置tabPanel的背景颜色
						html:'',
						listeners : {	
			                activate : function(tab) {
									Ext.Ajax.request({
										url : "admin/instance/variableData",
										params : {
											id : id
										},
										success : function(response) {
											if (response.responseText == "false" || response.responseText == "[{}]") {
												Ext.getCmp('Variable').body.update('没有流程数据'); 									
											} else {
												Ext.getCmp('Variable').body.update("<pre class='brush:js'>"
																+ eval("("
																		+ response.responseText
																		+ ")")[0].variableJsonString
																+ "</pre>");
													
												SyntaxHighlighter.highlight();
											}
										}
									});
								}
						},
					}