Add a specific class to all textboxes on the page that you want to have this functionality.
Then, use this code to apply the functionality to the elements that have the class:
window.onload = function() {
var elements = document.querySelectorAll('.yourClassName');
for(var i = 0, j = elements.length; i < j; i++) {
var element = elements[i];
element.onfocus = function() {
this.value = '';
this.style.color = 'black';
};
element.onblur = function() {
if(this.value == '') {
this.value = this.getAttribute('defaultValue');
this.style.color = 'grey';
}
};
element.onblur();
}
};
Working example: http://jsfiddle.net/6TmGA/1/