How to avoid multiple submissions of a form on client side?

Hi jhon,
I am assuming by your mentioned tags that you are working in asp.net so you can use following code.
In markup on client event you can call your validate() method as shown.

 
<asp:Button ID="btnsubmit" runat="server" OnClick="btnsubmit_Click" OnClientClick="return Validate();" />

Then you can update your validate() method by adding following chucks in your code.
What it will do is when your client side validation is true then it will add a class "btnDisabled" and once the class is added it will stop submitting the form again. After successful submission if it is landing on the same page then you need to explicitly remove "btnDisabled" class for next submission.

 
 function Validate() {
        var isValid = true;
        if ($("#<%=btnsubmit.ClientID%>").hasClass("btnDisabled")) {
            return false;
        }
      //Here you can added your client side validations
        if (isValid === true) {
            $("#<%=btnsubmit.ClientID%>").addClass("btnDisabled")
         }
        return isValid;
    }