How to get .change trigger to work on wordpress admin.php [duplicate]

Question

Possible Duplicate:
$ not defined using jQuery in Wordpress

Ok, so I'm having some trouble here. I'm customizing a plugin. I need a text field to automatically populate with the text of a drop down menu when an option is selected. The ID's of both elements are created on age load via php; however the IDs do not change. The id for the is "field_new_post_category" and the id of the text field is "post_title" This is what I have so far:

<script type='text/javascript'>//<![CDATA[ 
$(function(){
$(document).ready(function(){
    $("#field_new_post_category").change(function(){
        $("#post_title").val($(this).find("option:selected").text());
    });
});
});//]]>  
</script>
<select name="field_new_post_category" id="field_new_post_category" class="categoriesBox">
<option class="level-0" value="1">Main Category</option>
<option class="level-1" value="5">&nbsp;&nbsp;&nbsp;sub-category</option>
<option class="level-2" value="7">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sub-sub-category</option>
</select>

<input type="text" id="post_title" class="span5" name="post_title" value="Campaign Title" readonly="readonly"/>

I have this working well in a JSFiddle here: http://jsfiddle.net/XVDH2/39/

The trouble is that when I put it all together in Wordpress, it doesn't work. Simply nothing. I make the selection and nothing changes.

Thanks for any help you might be able to offer. :)

-Chase

Answer 1

"TypeError: $ is not a function "

error shows up when either jQuery is not loaded or the jQuery object is not assigned to $. Possible solutions are

1. Try including jQuery wp_enqueue_script('jquery'). (you can check its inclusion by typing 'jQuery' in console and pressing Enter)
2. If it is already loaded. use "jQuery" instead of "$"

So, your code will look like this

jQuery(function(){
jQuery(document).ready(function(){
    jQuery("#field_new_post_category").change(function(){
        jQuery("#post_title").val(jQuery(this).find("option:selected").text());
    });
});
});

hope, it works