jQuery.fn.maxLength = function(max){       return this.each(function(){          var type = this.tagName.toLowerCase();           var inputType = this.type? this.type.toLowerCase() : null;           if(type == "input" && inputType == "text" || inputType == "password"){               //Apply the standard maxLength              // http://www.sharejs.com              this.maxLength = max;           } else if(type == "textarea"){              this.onkeypress = function(e){                   var ob = e || event;                   var keyCode = ob.keyCode;                   var hasSelection = document.selection? document.selection.createRange().text.length > 0 :this.selectionStart != this.selectionEnd;                   return !(this.value.length >= max && (keyCode > 50 || keyCode == 32 || keyCode == 0 || keyCode == 13) &&!ob.ctrlKey && !ob.altKey && !hasSelection);               };               this.onkeyup = function(){                   if(this.value.length > max){                       this.value = this.value.substring(0,max);                   }               };          }      });  };     //用法 www.open-open.com/code  $('#mytextarea').maxLength(500);