本文转自:http://naspinski.net/post/jQuery-TextBox-Water-Mark-with-aspnet.aspx
I stole majority of this code from
http://www.aspcode.net/A-watermark-texbox-with-JQuery-and-aspnet.aspx
but I added a bit to make it swap css classes as well
$().ready(function() { swapValues = []; $(".wm").each(function(i) { swapValues[i] = $(this).val(); $(this).focus(function() { if ($(this).val() == swapValues[i]) { $(this).val("").removeClass("watermark") } }).blur(function() { if ($.trim($(this).val()) == "") { $(this).val(swapValues[i]).addClass("watermark") } }) }) }); To use it, make sure your TextBox has (one of) it's css classes set to "wm". If you want a seperate style to be applied add that initially as well, in my example, it swaps "watermark" in and out as a css class. <asp:TextBox ID="txt" runat="server" Text="this is the watermark" CssClass="wm watermark" />