ASP.NET calling Javascript for validation

Gurus, I wanted to call Javascript for validation. If the validation fails, do not submit data form.
I added a HIDDEN field where the javascript changes it.  Here is what I came up with using visual basic.

If there is a better way, please advise.

TIA

'' code behind Public Class test_Form3Post Inherits System.Web.UI.Page Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim strtime As String strtime = DateTime.Now txtcurrtime.Text = strtime End Sub Protected Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click Dim strhidd2 As String strhidd2 = hidd2.Value If strhidd2 = "0" Or strhidd2 = "1" Then Else strhidd2 = "0" End If If strhidd2 = "1" Then txtc ...