WordPress plugin development

One-off background tasks with wp_schedule_single_event() wp_schedule_event() creates tasks that repeat forever. Many tasks should run only once, at a certain time: a follow-up email a day after registration, a cleanup an hour after an import, a reminder before an event. wp_schedule_single_event() does that: it runs a hook once at the given time and removes the…

Enqueue scripts and styles correctly in WordPress Adding JavaScript and CSS with <script> and <link> tags right in header.php is one of the most common mistakes of developers who come to WordPress from static HTML. It works, but it bypasses the WordPress asset system: no dependencies (your script may run before jQuery), duplicates (a plugin…

Create, update and assign terms in code: wp_insert_term() and wp_set_post_terms() Imports and migrations need to create categories and other terms in code, often with a hierarchy, and then assign them to posts. WordPress has functions for both: wp_insert_term(), wp_update_term() and wp_delete_term() manage the terms, wp_set_post_terms() and wp_set_object_terms() attach them to posts. The details that matter…

Multisite: query all sites with get_sites() and switch_to_blog() In a Multisite network every site has its own posts, options and users’ roles, in its own set of tables. Code that runs on one site sees only that site’s data. To build something across the network, a list of the latest posts of all sites or…

Suggest privacy policy text from a plugin and link to the policy page Since WordPress 4.9.6 a site has an official privacy policy page, chosen in Settings → Privacy, and a “Privacy Policy Guide” with text suggestions from core and plugins. A plugin that collects personal data can add its own section to that guide…

PHP 8.0 for WordPress developers: match, named arguments, nullsafe and more PHP 8.0 was released on November 26, 2020. It brings the biggest set of language changes since PHP 7.0: the match expression, named arguments, the nullsafe operator, union types, constructor property promotion, and a JIT compiler. WordPress 5.6, due on December 8, ships with…

Remove actions and filters added by core, themes and plugins Customising WordPress is not only adding callbacks; often you need to remove one: the emoji scripts on a site that does not need them, a parent theme’s output, a plugin’s popup, a WooCommerce email you replaced. remove_action() and remove_filter() do that, but only when three…

Build an admin list table with WP_List_Table The lists of posts, pages, users and comments in the admin are all built with the WP_List_Table class: columns, sorting links, bulk actions, row actions, pagination. A plugin that shows its own records (form leads, log entries, imports) can extend the same class and get a screen that…

Create and update posts in code with wp_insert_post() wp_insert_post() and wp_update_post() create and change posts without the editor: in import scripts, WP-CLI commands, plugin activation (a default page), or a cron job that pulls content from an API. They take an array with the columns of the posts table and two helpers, meta_input and tax_input,…