Si desea hacerlo sin usar jquery o modenizer, puede usar el siguiente código:
(function(){
"use strict";
//shim for String's trim function..
function trim(string){
return string.trim ? string.trim() : string.replace(/^\s+|\s+$/g, "");
}
//returns whether the given element has the given class name..
function hasClassName(element, className){
//refactoring of Prototype's function..
var elClassName = element.className;
if(!elClassName)
return false;
var regex = new RegExp("(^|\\s)" + className + "(\\s|$)");
return regex.test(element.className);
}
function removeClassName(element, className){
//refactoring of Prototype's function..
var elClassName = element.className;
if(!elClassName)
return;
element.className = elClassName.replace(
new RegExp("(^|\\s+)" + className + "(\\s+|$)"), ' ');
}
function addClassName(element, className){
var elClassName = element.className;
if(elClassName)
element.className += " " + className;
else
element.className = className;
}
//strings to make event attachment x-browser..
var addEvent = document.addEventListener ?
'addEventListener' : 'attachEvent';
var eventPrefix = document.addEventListener ? '' : 'on';
//the class which is added when the placeholder is being used..
var placeHolderClassName = 'usingPlaceHolder';
//allows the given textField to use it's placeholder attribute
//as if it's functionality is supported natively..
window.placeHolder = function(textField){
//don't do anything if you get it for free..
if('placeholder' in document.createElement('input'))
return;
//don't do anything if the place holder attribute is not
//defined or is blank..
var placeHolder = textField.getAttribute('placeholder');
if(!placeHolder)
return;
//if it's just the empty string do nothing..
placeHolder = trim(placeHolder);
if(placeHolder === '')
return;
//called on blur - sets the value to the place holder if it's empty..
var onBlur = function(){
if(textField.value !== '') //a space is a valid input..
return;
textField.value = placeHolder;
addClassName(textField, placeHolderClassName);
};
//the blur event..
textField[addEvent](eventPrefix + 'blur', onBlur, false);
//the focus event - removes the place holder if required..
textField[addEvent](eventPrefix + 'focus', function(){
if(hasClassName(textField, placeHolderClassName)){
removeClassName(textField, placeHolderClassName);
textField.value = "";
}
}, false);
//the submit event on the form to which it's associated - if the
//placeholder is attached set the value to be empty..
var form = textField.form;
if(form){
form[addEvent](eventPrefix + 'submit', function(){
if(hasClassName(textField, placeHolderClassName))
textField.value = '';
}, false);
}
onBlur(); //call the onBlur to set it initially..
};
}());
Para cada campo de texto que desee usar, debe ejecutarlo placeHolder(HTMLInputElement), pero supongo que puede cambiarlo para adaptarlo. Además, hacerlo de esta manera, en lugar de solo en carga, significa que puede hacer que funcione para entradas que no están en el DOM cuando se carga la página.
Tenga en cuenta que esto funciona aplicando la clase: usingPlaceHolderal elemento de entrada, por lo que puede usar esto para darle estilo (por ejemplo, agregue la regla .usingPlaceHolder { color: #999; font-style: italic; }para que se vea mejor).