Custom javascript
If you want to use custom javascript you can use the onclientclick:
onclientclick="YourJSFunction()"
The server side code will execute when you return true.
<asp:Button ID="btnAddActivation" Text="Add New Validation" onclientclick="YouJSFunction()" OnCommand="AddNewActivation" runat="server"/>
See here for more info:
There are also built in validation controls that you could use for regular expression and required fields i.e.
RegularExpressionValidator
<asp:RegularExpressionValidator ControlToValidate="txtIso" runat="server" ValidationExpression="String" />
RequiredFieldValidator
<asp:RequiredFieldValidator id="RequiredFieldValidator1"
ControlToValidate="txtIso"
Text="Required Field!"
runat="server"/>
http://msdn.microsoft.com/en-us/library/5hbw267h(v=vs.85).aspx