var is = document.getElementsByTagName('input');
var dv = [];

for (var i=0,len=is.length;i<len;i++) {
	dv.push(is[i].value);
	is[i].onclick = function () {is[i].value='';};
	is[i].onblur = function() { if (!is[i].value) is[i].value = dv[i]; };
}