Best practices for WordPress plugin development

Slides for the first part of this tutorial presented on October 4th 2013 at PHPNW, Manchester, UK.
http://conference.phpnw.org.uk/phpnw13/
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With the release of WP3, WordPress has become a serious contender on the CMS market. The WordPress plugin system allows you to add functionality to WordPress in a snap and turn it into much more than ‘just a blogging platform’.
Learn how to develop for WordPress like a pro and take WordPress to the next level.
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Tutorial code:
https://github.com/jrfnl/wp-plugin-best-practices-demo

Transcript

1. Best practices for WordPress
   plugin development
   Tutorial @ PHPNW2013
   Juliette Reinders Folmer
   

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2. Juliette Reinders Folmer
   Email: juliette@adviesenzo.nl
   Web: http://www.adviesenzo.nl/
   LinkedIn: http://nl.linkedin.com/in/julietterf
   Twitter: http://twitter.com/jrf_nl
   GitHub: http://github.com/jrfnl/
   WordPress: http://profiles.wordpress.org/jrf
   

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7. Anatomy of WP
   Core
   Plugins
   Themes
   Languages
   Js Libraries
   Post Types
   Taxonomies
   Content areas:
   Front-end:
   Header
   Main (Loop)
   Sidebar (Widgets)
   Footer
   Back-end:
   Admin Bar
   Menu
   Post Types
   Metaboxes
   Settings pages
   

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9. Hooks
   Actions – do something
   Filters – filter someting and return the result
   See:
   Manual
   Hooks database:
   http://adambrown.info/p/wp_hooks
   Debug Bar - Action& filter hooks plugin
   

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11. The Loop
    if ( have_posts() ) {
    while ( have_posts() ) {
    the_post();
    //
    // Post Content here
    //
    } // end while
    } // end if
    ?>
    

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13. Don’t reinvent the wheel
    Dashboard Widgets API
    Database API
    HTTP API
    File Header API
    Filesystem API
    Heartbeat API
    Metadata API
    Options API
    Plugin API
    Quicktags API
    Rewrite API
    Settings API
    Shortcode API
    Theme modification API
    Theme customization API
    Transients API
    Widgets API
    XML-RPC WordPress
    API
    

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15. Avoid conflict
    function_exists()
    class_exists()
    Jquery no conflicts mode
    Use bundled libraries
    

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17. Be Unique
    PHP:
    Classes
    Functions
    global vars
    (global) constants
    WP:
    shortcodes
    option(s) / meta fields
    nonces
    settings pages
    custom post types
    hooks
    Filenames
    HTML/CSS:
    classes, ids
    Javascript:
    I18n object
    functions
    Multi-lingual
    I18n text domain
    Choose your plugin name carefully & implement consistently
    

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19. Be lazy, be lean
    Use the available is_...() functions
    Conditional loading of include files
    Conditional loading of css / js both on admin as
    well as frontend!
    Minify js and css
    New in WP3.6: has_shortcode()
    

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21. Be safe
    Check early & check often
    Validation all input
    sanitize_text_field(), sanitize_title(),
    sanitize_meta() etc function group
    Escape all output
    esc_html(), esc_attr(), esc_url(), esc_textarea(),
    esc_js() etc
    Use wp_nonce
    

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23. Be worldly
    GetText
    UTF-8
    Impact on data validation
    

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26. Don’t get discouraged
    WP_DEBUG constants
    Enable error logging!
    wp_config.php: @ini_set()
    set_error_handling() to a backtrace function
    Debug bar to the rescue
    JS console logging + plugin
    set_transient()
    Beware: Lots of templates which do not comply
    to the WP standards!
    

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31. Starting a plugin
    /*
    Plugin Name: Demo Quotes Plugin
    Plugin URI: https://github.com/jrfnl/wp-plugin-best-
    practices-demo
    Description: Demo plugin for WordPress Plugins Best
    Practices Tutorial
    Version: 1.0
    Author: Juliette Reinders Folmer
    Author URI: http://adviesenzo.nl/
    Text Domain: demo-quotes-plugin
    Domain Path: /languages/
    License: GPL v3
    */
    

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32. What every plugin needs
    Hook your functionality onto actions and filters
    Loading your localization files
    Load CSS
    Load JS
    Do something
    Add admin page or add to another admin page
    Help information
    Activation/ Upgrade routines
    Uninstall routines
    ...
    

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34. Hooks
    Offer your own action hooks
    Offer your own filter hooks
    Document using the @api tag
    

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36. To sum up:
    Use classes, class constants and statics
    Most plugins run as singletons
    Leave as small a footprint in the global
    namespace as possible
    Prefix ALL your css classes/ids, js functions and
    anything else in the global namespace
    Use WP functions – combined knowledge of
    thousands
    

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37. Credits
    Anatomy - Eva di Martino
    http://www.pureblacklove.com
    Bridge - Glenn Euloth
    http://www.flickr.com/photos/eulothg/4956082108/
    Conflict - Asaf Antman
    http://www.flickr.com/photos/asafantman/5134136997/
    Help - Green Kozi
    http://www.flickr.com/photos/themacinator/3445776069/
    Hooks - Raul Lieberwirth
    http://www.flickr.com/photos/lanier67/185311136/
    Hooks – Macroman (red background)
    http://www.flickr.com/photos/macroman/34644959/
    Alone – Jon
    http://www.flickr.com/photos/jb-london/3594171841/
    Fun - Justin Beckley
    http://www.flickr.com/photos/justinbeckleyphotography/8452437969/
    Lazy - Kevin Cauchi
    http://www.flickr.com/photos/kpcauchi/5376768095/
    Loop - Gabe Kinsman
    http://www.flickr.com/photos/auguris/5286612308/
    Security – kismihok
    http://www.flickr.com/photos/kismihok/9686252463/
    

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38. Credits
    Unique - Luca Volpi (leafs)
    http://www.flickr.com/photos/luca_volpi/2974346674/
    Unique - David Sprinks (birds)
    http://www.flickr.com/photos/davidspinks/4211976336/
    Wheel - Pauline Mak
    http://www.flickr.com/photos/__my__photos/5025541044/
    WordPress - mkhmarketing (crayons)
    http://www.flickr.com/photos/mkhmarketing/8469030267/
    WordPress - Tom Woodward (revolution)
    http://www.flickr.com/photos/bionicteaching/3048825267/
    WordPress - Saad Irfan (core, plugins, themes)
    http://www.flickr.com/photos/saadirfan/5722057280/
    CMS Landscape - Philippe Martin
    http://www.flickr.com/photos/lafabriquedeblogs/5997969999/
    World - Kenneth Lu
    http://www.flickr.com/photos/toasty/1540997910/
    Bike - Pauline Mak
    http://www.flickr.com/photos/__my__photos/6399028713/
    Daisies - Steve Wall
    http://www.flickr.com/photos/stevewall/4780035332/
    

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39. Keep in touch!
    (I’m self-employed, you can hire me ;-) )
    Juliette Reinders Folmer
    Email: juliette@adviesenzo.nl
    Web: http://www.adviesenzo.nl/
    LinkedIn: http://nl.linkedin.com/in/julietterf
    Twitter: http://twitter.com/jrf_nl
    GitHub: http://github.com/jrfnl/
    WordPress: http://profiles.wordpress.org/jrf
    Please rate this talk on joined.in/
    Endorsements and recommendations on LinkedIn are much
    appreciated too!
    

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