OnkeyPress attributes in TextBox using JavaScript

Here code shows how to use onkeypress in TextBox.When user write in textbox a Label show no. of charachter entered in TextBox

 function valid(txt,maxLen,lbl1)  
 {  
      lbl1.innerText=(txt.value.length+1);   
      if(txt.value.length > (maxLen-1))  
      {  
           alert("Entered Text reach at its maximum size..!");  
           return false;  
      }  
 }   
 txtFeedback.Attributes["onkeypress"] = "return valid(this,500," + Label1.ClientID + ")";  

Thanks & Regards
Santosh