Calling ajaxWatermark extender in javascript

i have a Ajax Control toolkit water mark extender for a search box which is there in a master page . Based on certain condition ,i would like to change this value from the child page which inhe开发者_Go百科rits from this master page .I want to do it in client side with jquery /javascript . Any ideas??

You can create a javascript function that change the watermark, andd just call it from your child page

function setWatermarkText(text)
{
  var watermark = $get('<%= WatermarkExtender.ClientID %>');
  watermark.set_Text("John Smith");
}