Executing jQuery in a plugin

Question

I have the following code in my plugin main file :

function my_function() {
?>
<script type="text/javascript"> 
    jQuery(function () {    
        alert('jQuery');
    });
</script>
<?php
}
add_action("wp_footer", "my_function");

My website does have jQuery loaded and operational (lots of features on my page use it and they work). Yet this alert() doesn't work. Why is that ?

Answer 1

That snippet 'works' for me.

Is the script being printed at the bottom of the page? More specifically, does your theme call wp_footer. All themes should, but not all themes do call wp_footer which breaks plugins which rely on it.

For the record - you should not print scripts directly to the page. WordPress has a great API for handling JavaScript enqueing and dependency handling. See this codex page.

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Answer 2

Because you just defined a function there. You didn't execute it or attached it to some event, to be executed when the event happens.

You probably want:

jQuery(document).ready(function($){
  alert('jQuery');
});

Now this function will run after the document has loaded.

And try to avoid inline scripts. Use wp_enqueue_script whenever possible.