How many times have you installed a plugin, integrated it with your theme, decide to uninstall it, but then forget to remove its function within the theme?
Once you’ve uninstalled a plugin, you have to go back to your WordPress theme to remove any trace of it, or else your blog would return “function doesn’t exist” errors.
In case you forget to remove all traces of a certain un-installed plugin, this is a quick tip to error-proof your future un-installation so your readers wouldn’t have to run across “function doesn’t exist” errors.
Let’s say you want to use the Author Highlight plugin, which adds a class to your comments, to style comments made by you. It wants you to add <?php author_highlight(); ?> to somewhere in the comments.php file. Instead of doing just that, here’s what you should add:
<?php if(function_exists(”author_highlight”)) author_highlight(); ?>
Don’t copy and paste the codes above, it will not work. Type it out.