Disable the button when Clicked

When there is no Attribute added for onclick the code will be:

btnSubmit.Attributes.Add("onclick", "this.disabled=true;" + GetPostBackEventReference(btnSubmit).ToString());

If onclick Attribute exists then:

var btn = document.getElementById('< %=btnSubmit.ClientID% >');
btn.disabled=true;
btn.style.color='#ADAA9C';
__doPostBack('btnSubmit','');

--We can add this on link/button
OnClientClick="this.disabled = true; this.value = 'Genrating Rep..';__doPostBack(this.name,'');"