[javascript] Placeholder in IE9

If you want to do it without using jquery or modenizer you can use the code below:

(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..
    };

}());

For each text field you want to use it for you need to run placeHolder(HTMLInputElement), but I guess you can just change that to suit! Also, doing it this way, rather than just on load means that you can make it work for inputs which aren't in the DOM when the page loads.

Note, that this works by applying the class: usingPlaceHolder to the input element, so you can use this to style it (e.g. add the rule .usingPlaceHolder { color: #999; font-style: italic; } to make it look better).