javascript - JQuery - $ is not defined

Question

I have a simple jquery click event

<script type="text/javascript">
    $(function() {
        $('#post').click(function() {
            alert("test"); 
        });
    });
</script>

and a jquery reference defined in the site.master

<script src="<%=ResolveUrl("~/Scripts/jquery-1.3.2.js")%>" type="text/javascript"></script>

I have checked that the script is being resolved correctly, I'm able to see the markup and view the script directly in firebug, so I must be being found. However, I am still getting:

$ is not defined

and none of the jquery works. I've also tried the various variations of this like $(document).ready and jQuery etc.

It's an MVC 2 app on .net 3.5, I'm sure I'm being really dense, everywhere on google says to check the file is referenced correctly, which I have checked and checked again, please advise! :/

Answer 1

That error can only be caused by one of three things:

1. Your JavaScript file is not being properly loaded into your page
2. You have a botched version of jQuery. This could happen because someone edited the core file, or a plugin may have overwritten the $ variable.
3. You have JavaScript running before the page is fully loaded, and as such, before jQuery is fully loaded.

First of all, ensure, what script is call properly, it should looks like

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>

and shouldn't have attributes async or defer.

Then you should check the Firebug net panel to see if the file is actually being loaded properly. If not, it will be highlighted red and will say "404" beside it. If the file is loading properly, that means that the issue is number 2.

Make sure all jQuery javascript code is being run inside a code block such as:

$(document).ready(function () {
  //your code here
});

This will ensure that your code is being loaded after jQuery has been initialized.

One final thing to check is to make sure that you are not loading any plugins before you load jQuery. Plugins extend the "$" object, so if you load a plugin before loading jQuery core, then you'll get the error you described.

Note: If you're loading code which does not require jQuery to run it does not need to be placed inside the jQuery ready handler. That code may be separated using document.readyState.