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Best Practice: Check if Function Exists When Adding in WordPress Theme

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Recently, a user asked us how to check if a PHP function exists before adding some new code to your WordPress site that relies on it.

The best part about WordPress is its flexibility, including the ability to add your own custom functions to your website. However, sometimes, your custom code may not work because the function it’s referring to does not exist anymore.

In this article, we will show you how to easily check if a function exists before adding it to your WordPress theme.

Checking if a function exists in WordPress

Why Add ‘If Function Exists’ to Your Custom Code?

WordPress is mainly written in the PHP programming language. PHP is a server-side programming language that runs on your WordPress hosting provider’s servers.

Because PHP code has to finish running before the page is loaded in your visitors’ browsers, there are certain limitations to it. One of those limitations is that if something goes wrong, it could prevent the whole page from loading.

In WordPress, if a missing function prevents the rest of the code from running, then it halts and displays a critical error or fatal error message.

WordPress critical error message

What can make a function suddenly stop working or go missing?

It’s a more common WordPress error than you might think.

For example, let’s say one of your WordPress plugins comes with a function that you have added to your theme’s header or footer area. Deactivating the plugin will make the function disappear and cause the critical error on your WordPress website.

That being said, let’s take a look at how to easily check if a function exists before executing it in your WordPress theme files.

Checking If a Function Exists in WordPress

Luckily, the PHP programming language comes with a built-in method to easily check the existence of a function before executing it.

Let’s say you have a WordPress function that displays the current time with timezone information. Here’s a sample code snippet that you can use to try it.

You can add it directly to your theme’s functions.php file or use a code snippet plugin such as WPCode (recommended). You can see our guide on how to easily add custom code in WordPress:

//display current time with timezone
function wpb_show_timezone() {
$better_time = current_time('F j, Y g:i a e');
echo "<p>The current time is " . $better_time ."</p>";

To call this function, you will need to add the following code anywhere in your WordPress theme where you want to display the current time.

<?php wpb_show_timezone(); ?>

This is how it looked on our testing website.

Function runs normally

Now, what would happen if the code responsible for executing this function disappears?

The call to the function will break your website like this.

Critical error in WordPress

Let’s add a check to make sure that this code only runs when the function exists.

Again, you will need to add the code directly to your theme’s functions.php file or use a code snippet plugin such as WPCode (recommended):

if( function_exists('wpb_show_timezone')) {
} else {
// do nothing

In this code, we are using the function_exists() function. This function checks if a function exists and returns True or False.

We then added an if-else condition to take appropriate action depending on the availability of the function.

Now, when the function is no longer available, the code will simply skip it, and WordPress will be able to load the rest of your website normally.

Missing function skipped

We hope this article helped you learn how to check if a function exists in WordPress. You may also want to see our complete WordPress troubleshooting guide or our expert picks for the best drag and drop WordPress page builders.

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Editorial Staff

Editorial Staff at WPBeginner is a team of WordPress experts led by Syed Balkhi with over 16 years of experience in WordPress, Web Hosting, eCommerce, SEO, and Marketing. Started in 2009, WPBeginner is now the largest free WordPress resource site in the industry and is often referred to as the Wikipedia for WordPress.

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4 CommentsLeave a Reply

  1. Syed Balkhi says

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  2. Joana Pereira says

    Good call Kovshenin. I know exactly what you mean because I was using a custom function with contact form 7 (to retrieve the ip address on each form) and every time the plugin was updated, the theme broke.

    Thanks for the tip

    Joana Pereira

  3. kovshenin says

    Right, only please stop checking for dynamic_sidebar with function_exists in WordPress themes, unless you need to support WordPress 2.2 and below, which I *highly* doubt. Also with the user photo plugin, the whole approach seems to be wrong and redundant to me, it looks like many developers are missing the whole point of pluggable functions…. Oh well :)

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