It's working fine in my Machine.
I think you may have another problem.
Here is my full code
function clicked() {
debugger;
var number = 100;
var tmp = "$$myText" + number + "$$";
alert(tmp);
}
<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="clicked();" />
It's giving alert of
$$myText100$$
Check you may have browser specific problem.
Please
vote and
Accept Answer if it Helped.