转义特殊字符防止xss攻击

		function symbolEscape(text){
            return text.replace(/[<>"&]/g, function(match, pos, originalText){
              switch(match){
                case "<": return "&lt;"; 
                case ">":return "&gt;";
                case "&":return "&amp;"; 
                case "\"":return "&quot;"; 
              } 
            }); 
          }