How to pass Source and Args parameters to Javascript function

function Custom(source,Args) {
            var txt = document.getElementById('<%=TextBox3.ClientID %>').value;
            if (txt == 2) {
                Args.IsValid = true;
                return;
            }
            source.innerText = "Enter 2";
            Args.IsValid = false;
            return ;

function ButtonFunc() {
            if (Custom()) { //What Parameter to pass for source and Args ??
                return true;
            }
            return false;
        }