Server side validations can be invoked using the Page.Validate() method. The status of the validation is set to the Page.IsValid property by the asp.net runtime.
protected void Page_Load(object sender, EventArgs e)
protected void button1_Click(object sender, EventArgs e)
if (!Page.IsValid) return;
//Do something if validation passes.
This server side validation works on all major browsers. I have tested on IE, FireFox and Netscape.