WordPress revolutionized the web development industry by eliminating the need for coding to create a website. It provides pre-built components which are required for building an interface and a user has only to pick and choose the desired elements. There are readymade themes which contain all the necessary items like pages and features that a specific interface will require. Then there are plugins which allow users to easily extend the functionality of their website. In case you want to use the CMS to build interfaces or develop themes or plugins, you must know about the WordPress hook system. Hooks, action, and filters are integral parts of the event-driven architecture of the open-source CMS. An event-driven architecture is a system which identifies events which alter a specific state and then react accordingly. This allows developers to fashion their creations without tinkering with the source code. Let us now discuss the hook system of the open-source CMS.
What Are Hooks?
A hook is an event which occurs during the execution of the functionality of the core, themes or plugins. They are called so because they let developers hook onto an event and then perform a specific action related to that particular occurrence. When WordPress starts running the execution, it checks whether any theme or plugin has registered a function to be performed at that point. When it finds that a function is registered, then it executes it at that point. This means that there is no need to alter the core code to add new functionality to an interface. Many people convert Website to WordPress only because it provides such an easy way to add new features. There are two kinds of hooks namely, actions and filters.
Action hooks can be thought of as locations where a function or a code can hook into. If you have used analytics you must have added a tracking code to the footer of your interface. wp_footer is the action hook where the specified function, which in this case, is the tracking code must be operationalized. Actions can be used when you want to alter global variables or the parameters passed to the hook function. Action hooks are added in the following manner:
add_action( $hook, $function_to_add, $priority, $accepted_args );
Here “$hook” is the action on to which you want to hook and “$function_to_add” is the specific function created by you which must be performed when the hook is activated. In case, you want to remove a hook, then you must use the following format:
remove_action( $hook, $function_to_remove, $priority);
You can find the complete list of action hooks in the Plugin API section of the WordPress Codex. Let’s take a look at an example to understand actions. Let’s say you want to publish a post on social networks as soon as it is uploaded on your website. Now, it is clear that you will have to modify the behavior when the Publish button on a post is pressed. The action hook that you need to hook onto in this case is “publish_post”. The following code shows how the action has been hooked on to execute a function called “publish post to social media”.
Filter hooks are functions through which WordPress passes data. This passing through occurs at specific points during the execution just before an action is executed with the help of the data. This lets developers to alter the behavior displayed by a specific function. Filters, like actions, receive data through various parameters. Both types of hooks are mostly doing the same thing but they are different. A filter hook must return a value while an action hook does not need to do so. You can use filters for the same purpose as you used actions for but you will need to modify the value of the specified data parameter. Filters can be added in this manner:
add_filter( $hook, $function_to_add, $priority, $accepted_args );
Here “$hook” is the filter you want to use and “$function_to_add” is the function that you will specify. Removing a filter hook can be done in the following manner:
remove_filter( $hook, $function_to_remove, $priority);
Remember that $priority is an optional argument. All the filter hooks are listed in the WordPress Codex. We will now show how filters are actually used by providing an example. Let’s say a person wants to add the name of her firm in the titles of every WordPress post. Then she can use a filter which will do the needful whenever a title is accessed. In the following code, “title_save_pre” is the filter which is modifying the title and returning it.
You will now have a fair idea of how hooks can be used to add custom functionality to your website. However, if the topic is too technical for you, then you must hire WordPress development services to add the features.