How to write Client Validation code on Clientside. like validating Textbox to enter only age using javascript

Question

I want to write code in javascript to valid my textbox at client side in my asp.net application.
I write code javascipt code taking refference from this link
http://www.c-sharpcorner.com/uploadfile/purankaushal/103222006013805am/1.aspx

but when i write code as it is my program it showing error in

Error    4    ; expected    c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\master_practice\faf8de5c\f8430d80\App_Web_qiup44vn.0.cs    838    121
Error    9    ; expected    c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\master_practice\faf8de5c\f8430d80\App_Web_qiup44vn.0.cs    846    18    

 like 15 error in    App_Web_qiup44vn.0.cs file.