Thomas Fuchs has created defaultValueActsAsHint, an implementation of the Input Prompt pattern. I like the idea to have this function, but I use dojo and so I implement it for dojo:
function defaultValueActAsHint(elem) {
var element = elem;
element.defaultValue = element.value;
dojo.attr(element, "class", "hint");
dojo.connect(elem, "onfocus", null, function() {
if(element.defaultValue != element.value) return;
dojo.attr(element, "class", "");
element.value = '';
});
dojo.connect(elem, "onblur", null, function() {
if(element.value != '') return;
dojo.attr(element, "class", "hint");
element.value = element.defaultValue;
});
}