Javascript validations in asp.net

This simple program will guide how to do client side validation of Form in JavaScript.
In this just make a form as follows:

1. Name : <asp:TextBox ID="txtName" />
2. Email : <asp:TextBox ID="txtEmail" />
3. Web URL : <asp:TextBox ID="txtWebUrl" />
4. Zip : <asp:TextBox ID="txtZip" />
5. <asp:Button ID="btnSubmit" OnClientClick=" return validate()" runat="server" Text="Submit" />

Now on the source code of this form in script tag write the following code:
<script language="javascript" type="text/javascript">
function validate()
{      if (document.getElementById("<%=txtName.ClientID%>").value=="")
      {                 alert("Name Feild can not be blank");
                 document.getElementById("<%=txtName.ClientID%>").focus();                 return false;
      }      if(document.getElementById("<%=txtEmail.ClientID %>").value=="")
      {
                 alert("Email id can not be blank");                document.getElementById("<%=txtEmail.ClientID %>").focus();                return false;
      }     var emailPat = /^(\".*\"|[A-Za-z]\w*)@(\[\d{1,3}(\.\d{1,3}){3}]|[A-Za-z]\w*(\.[A-Za-z]\w*)+)$/;     var emailid=document.getElementById("<%=txtEmail.ClientID %>").value;     var matchArray = emailid.match(emailPat);     if (matchArray == null)
    {
               alert("Your email address seems incorrect. Please try again.");
               document.getElementById("<%=txtEmail.ClientID %>").focus();               return false;
    }    if(document.getElementById("<%=txtWebURL.ClientID %>").value=="")
    {
               alert("Web URL can not be blank");
               document.getElementById("<%=txtWebURL.ClientID %>").value="http://"               document.getElementById("<%=txtWebURL.ClientID %>").focus();               return false;
    }    var Url="^[A-Za-z]+://[A-Za-z0-9-_]+\\.[A-Za-z0-9-_%&\?\/.=]+$"    var tempURL=document.getElementById("<%=txtWebURL.ClientID%>").value;    var matchURL=tempURL.match(Url);     if(matchURL==null)
     {
               alert("Web URL does not look valid");
               document.getElementById("<%=txtWebURL.ClientID %>").focus();               return false;
     }     if (document.getElementById("<%=txtZIP.ClientID%>").value=="")
     {
               alert("Zip Code is not valid");
               document.getElementById("<%=txtZIP.ClientID%>").focus();               return false;
     }     var digits="0123456789";     var temp;     for (var i=0;i<document.getElementById("<%=txtZIP.ClientID %>").value.length;i++)
     {
               temp=document.getElementById("<%=txtZIP.ClientID%>").value.substring(i,i+1);               if (digits.indexOf(temp)==-1)
               {
                        alert("Please enter correct zip code");
                        document.getElementById("<%=txtZIP.ClientID%>").focus();                        return false;
               }
     }     return true;
}</script>
And in code behind file just write the below code.

 protected void Page_Load(object sender, EventArgs e)
    {
        btn_reg.Attributes.Add("onclick", "return validate()");
    }