Best practices for WordPress plugin development - PHPWorld

Presented on November 17th 2015 at PHPWorld, Washington D.C., USA.
https://world.phparch.com/
---------------------------------------------------------------
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." Custom post types, post formats, shortcodes, custom fields, and metaboxes are all ways to extend the functionality of WordPress. In this tutorial, we'll look at a number of best practices for building WordPress plugins and some common mistakes made. Bring your favorite plugin to improve, or start building your own.

Transcript

1. Best Practices for
   WordPress Plugin Development
   Tutorial by Juliette Reinders Folmer / @jrf_nl
   

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2. #phpworld
   

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3. Who Are You ?
   

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4. #phpworld
   Who Am I ?
   Self-employed,
   Independent
   Consultant
   Creator
   PHPCheatsheets
   phpcheatsheets.com
   Frequent
   Contributor to
   Open Source
   Projects
   

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5. #phpworld
   Agenda
   Introducing Best
   Practices
   Applying
   Best Practices
   Closing
   

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6. #phpworld
   Agenda
   Introducing Best
   Practices
   

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7. WordPress Basics
   

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8. #phpworld
   Anatomy of WordPress
   

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9. #phpworld
   Page
   footer
   Admin
   Bar
   Page
   content
   (loop)
   Page
   header
   (Invisible) HTML
   Sidebar
   containing
   widgets
   (Main)
   menu
   

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10. #phpworld
    Admin Bar
    (Invisible) HTML
    Admin
    footer
    Admin
    Menu
    1. Post
    types
    2. Custom-
    izations
    3. Extras
    Admin
    page
    (with
    dashboard
    widgets)
    

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11. #phpworld
    Anatomy of WordPress
    Functionality
     Core
     Plugins
     Themes
     Languages
     Js Libraries
    Content
     Post Types
     Taxonomies
     Widgets
     Users
     Meta data/custom fields
     Options
     Shortcodes
     OEmbeds
    

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12. #phpworld
    Hooks
    

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13. #phpworld
    Hooks
    See:
     WordPress Codex & Developer Reference
     Hooks database: http://adambrown.info/p/wp_hooks
     Debug Bar – Action & filter hooks plugin
    

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14. #phpworld
    Hooking into WP
    apply_filter( 'hook_name', 'function_name',
    $priority = 10, $accepted_args = 1 );
    add_action( 'hook_name', 'function_name',
    $priority = 10, $accepted_args = 1 );
    add_action( 'hook_name', array( $this, 'method_name' ),
    $priority = 10, $accepted_args = 1 );
    add_action( 'hook_name',
    array( __CLASS__, 'static_method_name' ),
    $priority = 10, $accepted_args = 1 );
    

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15. #phpworld
    Action Hooks Front-end
    muplugins
    _loaded
    plugins
    _loaded
    setup
    _theme
    set_current
    _user
    after_setup
    _theme
    init wp_loaded
    parse
    _request
    posts
    _selection
    wp
    wp_head the_post wp_meta wp_footer
    admin_bar
    _menu
    

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16. #phpworld
    Action Hooks Back-end
    muplugins
    _loaded
    plugins
    _loaded
    setup
    _theme
    set_current
    _user
    after_setup
    _theme
    init wp_loaded
    admin
    _menu
    admin_init
    current
    _screen
    load-
    {page}
    posts
    _selection
    wp
    admin
    _head
    admin_bar
    _menu
    admin
    _notices
    the_post
    admin
    _footer
    

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17. #phpworld
    Action Hooks Back-end
    muplugins
    _loaded
    plugins
    _loaded
    setup
    _theme
    set_current
    _user
    after_setup
    _theme
    init wp_loaded
    admin
    _menu
    admin_init
    current
    _screen
    load-
    {page}
    posts
    _selection
    wp
    admin
    _head
    admin_bar
    _menu
    admin
    _notices
    the_post
    admin
    _footer
    

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18. #phpworld
    The Loop
    

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19. #phpworld
    The Loop
    if ( have_posts() ) :
    while ( have_posts() ) : the_post();
    //
    // Post Content here
    // the_title()
    // the_content()
    // the_permalink()
    // ...
    endwhile;
    endif;
    

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20. #phpworld
    Putting the
    Pieces Together
    

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21. #phpworld
    Putting the Pieces Together
    wp-config.php
    Must-use plugins
    Plugins
    • [MS] Network-activated plugins
    • Site-activated plugins
    Theme
    • Child-theme functions.php
    • Parent-theme functions.php
    

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22. Doing It Wrong ™
    

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23. #phpworld
    Doing It Wrong
    function wrap_content( $content ) {
    echo '' .
    $content . '';
    }
    add_filter( 'the_content', 'wrap_content' );
    

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24. #phpworld
    Doing It Right
    function my_prefix_wrap_content( $content ) {
    return '' .
    $content . '';
    }
    add_filter( 'the_content',
    'my_prefix_wrap_content' );
    

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25. #phpworld
    Doing It Wrong
    function prefix_add_hooks() {
    add_action( 'init', 'prefix_my_init' );
    add_action( 'admin_init', 'prefix_my_admin_init' );
    }
    add_action( 'wp', 'prefix_add_hooks' );
    

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26. #phpworld
    Doing It Right
    function prefix_add_hooks() {
    add_action( 'init', 'prefix_my_init' );
    add_action( 'admin_init', 'prefix_my_admin_init' );
    }
    add_action( 'plugins_loaded', 'prefix_add_hooks' );
    

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27. #phpworld
    Doing It Wrong
    function unique_prefix_content( $content ) {
    return $content .
    'Copyright Company 2010-' .
    date( 'Y' ) .
    '.';
    }
    add_filter( 'the_content', 'unique_prefix_content' );
    

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28. #phpworld
    Doing It Right
    function unique_prefix_content( $content ) {
    return $content . '' .
    sprintf(
    /* Translators: 1: Company Name, 2: Year. */
    esc_html__( 'Copyright %1$s %2$s.', 'text-domain' ),
    'Company',
    date_i18n( 'Y', get_the_date( 'U' ) )
    ) .
    '';
    }
    add_filter( 'the_content', 'unique_prefix_content' );
    

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29. #phpworld
    Doing It Wrong
    function unique_prefix_title( $title, $id ) {
    $post = get_post( $id );
    if ( $post->post_type == 'my_cpt' ) {
    $title = sprintf(
    esc_html__( '%s (My Custom Type)', 'text-domain' ),
    $title
    );
    }
    return $title;
    }
    add_filter( 'the_title', 'unique_prefix_title' );
    

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30. #phpworld
    Doing It Right
    function unique_prefix_title( $title, $id ) {
    $post = get_post( $id );
    if ( ! empty( $post->post_type ) &&
    'my_cpt' === $post->post_type ) {
    $title = sprintf(
    esc_html__( '%s (My Custom Type)', 'text-domain' ),
    $title
    );
    }
    return $title;
    }
    add_filter( 'the_title', 'unique_prefix_title', 10, 2 );
    

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31. #phpworld
    Doing It Wrong
    public function add_settings_link( $links, $file ) {
    if ( plugin_basename( __FILE__ ) === $file ) {
    $mylinks = array(
    'Settings',
    );
    $links = array_merge( $links, $mylinks );
    }
    return $links;
    }
    add_filter( 'plugin_action_links',
    array( $this, 'add_settings_link' ), 10, 2 );
    

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32. #phpworld
    Doing It Right
    public function add_settings_link( $links ) {
    if ( current_user_can( 'manage_options' ) ) {
    $links[] = sprintf(
    '%3$s',
    esc_url( $this->settings_url ),
    esc_attr__( 'Plugin-name Settings', 'text-d..n'),
    esc_html__( 'Settings', 'text-domain' ) );
    }
    return $links;
    }
    add_filter(
    'plugin_action_links_' . plugin_basename( __FILE__ ),
    array( $this, 'add_settings_link' ) );
    

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33. #phpworld
    Doing It Wrong
    function my_prefix_scripts() {
    echo '
    3.0/jquery.min.js">
    plugin/js/my-jquery-dependant-script.js' ) .
    '">';
    }
    add_action( 'wp_head', 'my_prefix_scripts' );
    

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34. #phpworld
    Doing It Right
    function my_prefix_scripts() {
    $suffix = ( ( defined( 'SCRIPT_DEBUG' ) &&
    true === SCRIPT_DEBUG ) ? '' : '.min' );
    wp_enqueue_script(
    'my-plugin-js', // ID.
    plugins_url( 'js/my-script' . $suffix . '.js', __FILE__
    ), // URL.
    array( 'jquery' ), // Dependants.
    PLUGIN_VERSION, // Version.
    true // Load in footer ?
    );
    }
    add_action( 'wp_enqueue_scripts', 'my_prefix_scripts' );
    

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35. #phpworld
    Doing It Wrong
    public function filter_featured_image( $value, $object_id,
    $meta_key, $single ) {
    if ( $meta_key === '_thumbnail_id' && is_home() ) {
    $field = 'frontpageimage';
    $meta_value = get_post_meta( $object_id, $field, $single );
    $value = (int) $meta_value;
    }
    return $value;
    }
    add_filter( 'get_post_metadata',
    array( $this, 'filter_featured_image' ), 10, 4 );
    

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36. #phpworld
    Doing It Right
    public function filter_featured_image( $value, $object_id, $meta_key ) {
    if ( $meta_key === '_thumbnail_id' && is_home() ) {
    $field = 'frontpageimage';
    remove_filter( 'get_post_metadata',
    array( $this, 'filter_featured_image' ), 10 );
    $meta_value = get_post_meta( $object_id, $field, true );
    add_filter( 'get_post_metadata',
    array( $this, 'filter_featured_image' ), 10, 3 );
    if ( is_numeric( $meta_value ) && 0 < (int) $meta_value ) {
    $value = (int) $meta_value;
    } }
    return $value;
    }
    add_filter( 'get_post_metadata', array( $this, 'filter_featured_image' ),
    10, 3 );
    

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37. #phpworld
    Doing It Wrong
    function schedule_my_cron_job() {
    wp_schedule_event(
    time(),
    'hourly',
    'my_cron_function‘
    );
    }
    add_action( 'init', 'schedule_my_cron_job' );
    

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38. #phpworld
    Doing It Right
    function schedule_my_cron_job() {
    if ( ! wp_next_scheduled( 'my_cron_function' ) ) {
    wp_schedule_event(
    time(),
    'hourly',
    'my_cron_function'
    );
    }
    }
    register_activation_hook( __FILE__ ,
    schedule_my_cron_job' );
    

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39. Best Practices
    

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40. #phpworld
    Know Your Hooks
    

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41. #phpworld
    Know Your Hooks
    Hook
    Order
    Actions
    vs
    Filters
    Parameters Priority
    

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42. #phpworld
    Don’t Reinvent the Wheel
    

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43. #phpworld
    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
    REST API * Rewrite API Settings API Shortcode API
    Theme
    modification
    API
    Theme
    customization
    API
    Transients API Widgets API
    XML-RPC
    WordPress API
    * Expected in WP 4.4
    

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44. #phpworld
    Use WP Functions
    PHP
     mysqli_...()
     file_put_contents()
     json_encode()
     mail()
     unserialize()
     htmlspecialchars()
     add/stripslashes()
     strtotime() / date()
     http_build_query()
     $_SERVER['HTTPS']
    ...
    WP
     $wpdb->....()
     $wp_filesystem->put_contents()
     wp_json_encode()
     wp_mail()
     maybe_unserialize()
     esc_html()
     wp_unslash()
     mysql2date() / current_time()
     add_query_arg()
     is_ssl()
    ...
    (I mean it!)
    

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45. #phpworld
    Avoid Conflict
    

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46. #phpworld
    Avoid Conflict
    function_exists() class_exists()
    Jquery no
    conflicts mode
    Use bundled
    libraries
    

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47. #phpworld
    Libraries shipped with WP
    json2 /wp-includes/js/json2.js
    underscore /wp-includes/js/underscore.js
    backbone /wp-includes/js/backbone.js
    prototype // via googleapis.com
    scriptaculous-root // via googleapis.com
    scriptaculous-builder // via googleapis.com
    scriptaculous-dragdrop // via googleapis.com
    scriptaculous-effects // via googleapis.com
    scriptaculous-slider // via googleapis.com
    scriptaculous-sound // via googleapis.com
    scriptaculous-controls // via googleapis.com
    cropper /wp-includes/js/crop/cropper.js
    swfobject /wp-includes/js/swfobject.js
    plupload /wp-includes/js/plupload/plupload.full.min.js
    plupload-handlers /wp-includes/js/plupload/handlers.js
    wp-plupload /wp-includes/js/plupload/wp-plupload.js
    swfupload /wp-includes/js/swfupload/swfupload.js
    swfupload-swfobject /wp-includes/js/swfupload/plugins/swfupload.swfobject.js
    swfupload-queue /wp-includes/js/swfupload/plugins/swfupload.queue.js
    swfupload-speed /wp-includes/js/swfupload/plugins/swfupload.speed.js
    swfupload-handlers /wp-includes/js/swfupload/handlers.js
    comment-reply /wp-includes/js/comment-reply.js
    quicktags /wp-includes/js/quicktags.js
    colorpicker /wp-includes/js/colorpicker.js
    editor /wp-admin/js/editor.js
    wp-ajax-response /wp-includes/js/wp-ajax-response.js
    wp-util /wp-includes/js/wp-util.js
    wp-backbone /wp-includes/js/wp-backbone.js
    revisions /wp-admin/js/revisions.js
    imgareaselect /wp-includes/js/imgareaselect/jquery.imgareaselect.js
    mediaelement /wp-includes/js/mediaelement/mediaelement-....js
    wp-mediaelement /wp-includes/js/mediaelement/wp-mediaelement.js
    froogaloop /wp-includes/js/mediaelement/froogaloop.min.js
    wp-playlist /wp-includes/js/mediaelement/wp-playlist.js
    zxcvbn-async /wp-includes/js/zxcvbn-async.js
    password-strength-meter /wp-admin/js/password-strength-meter.js
    jquery-core /wp-includes/js/jquery/jquery.js
    jquery-migrate /wp-includes/js/jquery/jquery-migrate.js
    jquery-ui-core /wp-includes/js/jquery/ui/core.js
    jquery-effects-core /wp-includes/js/jquery/ui/effect.js
    jquery-effects-blind /wp-includes/js/jquery/ui/effect-blind.js
    jquery-effects-bounce /wp-includes/js/jquery/ui/effect-bounce.js
    jquery-effects-clip /wp-includes/js/jquery/ui/effect-clip.js
    jquery-effects-drop /wp-includes/js/jquery/ui/effect-drop.js
    jquery-effects-explode /wp-includes/js/jquery/ui/effect-explode.js
    jquery-effects-fade /wp-includes/js/jquery/ui/effect-fade.js
    jquery-effects-fold /wp-includes/js/jquery/ui/effect-fold.js
    jquery-effects-highlight /wp-includes/js/jquery/ui/effect-highlight.js
    jquery-effects-puff /wp-includes/js/jquery/ui/effect-puff.js
    jquery-effects-pulsate /wp-includes/js/jquery/ui/effect-pulsate.js
    jquery-effects-scale /wp-includes/js/jquery/ui/effect-scale.js
    jquery-effects-shake /wp-includes/js/jquery/ui/effect-shake.js
    jquery-effects-size /wp-includes/js/jquery/ui/effect-size.js
    jquery-effects-slide /wp-includes/js/jquery/ui/effect-slide.js
    jquery-effects-transfer /wp-includes/js/jquery/ui/effect-transfer.js
    jquery-ui-accordion /wp-includes/js/jquery/ui/accordion.js
    jquery-ui-autocomplete /wp-includes/js/jquery/ui/autocomplete.js
    jquery-ui-button /wp-includes/js/jquery/ui/button.js
    jquery-ui-datepicker /wp-includes/js/jquery/ui/datepicker.js
    jquery-ui-dialog /wp-includes/js/jquery/ui/dialog.js
    jquery-ui-draggable /wp-includes/js/jquery/ui/draggable.js
    jquery-ui-droppable /wp-includes/js/jquery/ui/droppable.js
    jquery-ui-menu /wp-includes/js/jquery/ui/menu.js
    jquery-ui-mouse /wp-includes/js/jquery/ui/mouse.js
    jquery-ui-position /wp-includes/js/jquery/ui/position.js
    jquery-ui-progressbar /wp-includes/js/jquery/ui/progressbar.js
    jquery-ui-resizable /wp-includes/js/jquery/ui/resizable.js
    jquery-ui-selectable /wp-includes/js/jquery/ui/selectable.js
    jquery-ui-selectmenu /wp-includes/js/jquery/ui/selectmenu.js
    jquery-ui-slider /wp-includes/js/jquery/ui/slider.js
    jquery-ui-sortable /wp-includes/js/jquery/ui/sortable.js
    jquery-ui-spinner /wp-includes/js/jquery/ui/spinner.js
    

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48. #phpworld
    Be Unique
    

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49. #phpworld
    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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50. #phpworld
    Be Lazy, Be Lean
    

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51. #phpworld
    Be Lazy, Be Lean
    is_...()
    functions
    Conditional
    loading
    Hook in Include files css / js
    Minify
    

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52. #phpworld
    Be Safe
    

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53. #phpworld
    Be Safe
    Check early &
    check often
    current_user_can()
    Validation
    all input
    sanitize_text_field(), sanitize_title(),
    sanitize_meta(), sanitize_user() etc
    Prepare all
    queries
    $wpdb->prepare()
    Escape all
    output
    wp_kses(), esc_html(), esc_attr(),
    esc_url(), esc_textarea(), esc_js() etc
    Use
    wp_nonce
    wp_create_nonce(), wp_nonce_url(),
    wp_nonce_field(), wp_verify_nonce(),
    check_admin_referer(), check_ajax_referer()
    

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54. #phpworld
    Be Wordly
    

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55. #phpworld
    Be Worldly
     GetText
    load_plugin_textdomain( 'my_plugin', false,
    plugin_basename( dirname( __FILE__ ) ) . '/languages' );
    wp_kses_post( sprintf(
    __( 'Post updated. View post',
    'my_plugin' ),
    esc_url( get_permalink( $post_ID ) )
    ) );
    esc_html__( 'Custom field updated.', 'my_plugin' );
    

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56. #phpworld
    Be Worldly
     GetText
    load_plugin_textdomain( 'my_plugin', false,
    plugin_basename( dirname( __FILE__ ) ) . '/languages' );
    wp_kses_post( sprintf(
    __( 'Post updated. View post',
    'my_plugin' ),
    esc_url( get_permalink( $post_ID ) )
    ) );
    esc_html__( 'Custom field updated.', 'my_plugin' );
    

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57. #phpworld
    Be Worldly
     GetText
     Not only UTF-8
    seems_utf8( $str )
    wp_check_invalid_utf8( $string, $strip = false )
    utf8_uri_encode( $utf8_string, $length = 0 )
    convert_chars( $content )
    

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58. #phpworld
    I18n Quiz Time
    http://is.gd/WRLP9C
    (https://developer.wordpress.com/2015/04/23/
    wordpress-developers-test-your-i18n-
    internationalization-knowledge/)
    

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59. #phpworld
    Let Others Hook In
    

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60. #phpworld
    Let Others Hook In
    do_action( 'my_unique_action_hook', $var_to_pass );
    $filtered_var = apply_filters(
    'my_unique_filter_hook',
    $var_to_pass,
    $context_var,
    $another_context_var
    );
    

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61. #phpworld
    Make it Beautiful
    

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62. #phpworld
    

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63. Developing & Debugging
    

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64. #phpworld
    Don’t Get Discouraged
    WP_DEBUG
    Error
    logging!
    JS
    console
    logging
    set_
    transient()
    

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65. #phpworld
    Useful Plugins
    Debug Bar +
    Extensions
    Developer Pig Latin
    User Switching
    Log
    Deprecated
    Notices
    What’s
    Running
    Demo Data Theme Check RTL Tester
    

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66. #phpworld
    Helpful Infrastructure
    WordPress Coding Standards CS
    WP Unit Testing Framework
    Varying Vagrant Vagrants
    WP CLI
    Generate WP
    WP Gear
    WPackagist vs TGMPA
    

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67. #phpworld
    

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68. #phpworld
    Agenda
    Applying
    Best Practices
    

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69. Let’s Make Things Better
    

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70. #phpworld
    “
    ”
    To be prepared is half
    the victory.
    - Miguel de Cervantes
    

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71. #phpworld
    Let’s Make Things Better
    Copyrighted
    Post
    Easy Bootstrap
    Shortcode
    Login Logout Search Meter
    

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72. #phpworld
    Useful Resources
    Codex
    Developer
    Reference
    Source code
    (collection of
    best practices)
    Hook
    database
    Demo Quotes
    plugin
    (including
    handbooks!)
    

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73. #phpworld
    Agenda
    Closing
    

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74. Stay Involved
    

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75. #phpworld
    Help someone who’s
    struggling
    

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76. #phpworld
    Find an abandoned project
    

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77. #phpworld
    Have fun!
    

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78. #phpworld
    Image Credits
     WordPress - mkhmarketing (crayons)
    http://www.flickr.com/photos/mkhmarketing/8469030267/
     Billie Holiday – William P. Gottlieb
    http://lcweb2.loc.gov/diglib/ihas/loc.natlib.gottlieb.04251/default.html
     Anatomy - Eva di Martino
    http://www.pureblacklove.com
     Hooks - Raul Lieberwirth
    http://www.flickr.com/photos/lanier67/185311136/
     Loop - Gabe Kinsman
    http://www.flickr.com/photos/auguris/5286612308/
     Dominos – George Hodan
    http://www.publicdomainpictures.net/view-image.php?image=30522&picture=domino
     Hooks - Melissa Maples
    http://www.flickr.com/photos/melissamaples/3093966940/
     Wheel - Pauline Mak
    http://www.flickr.com/photos/__my__photos/5025541044/
     Conflict - Asaf Antman
    http://www.flickr.com/photos/asafantman/5134136997/
     Unique - Luca Volpi (leafs)
    http://www.flickr.com/photos/luca_volpi/2974346674/
     Lazy - Kevin Cauchi
    http://www.flickr.com/photos/kpcauchi/5376768095/
    

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79. #phpworld
    Image Credits
     Security – kismihok
    http://www.flickr.com/photos/kismihok/9686252463/
     World - Kenneth Lu
    http://www.flickr.com/photos/toasty/1540997910/
     Hooks – Macroman (red background)
    http://www.flickr.com/photos/macroman/34644959/
     Daisies - Steve Wall
    http://www.flickr.com/photos/stevewall/4780035332/
     Alone – Jon
    http://www.flickr.com/photos/jb-london/3594171841/
     Breaktime - Iryna Yeroshko
    https://www.flickr.com/photos/mandarina94/6389984357/
     Help - Green Kozi
    http://www.flickr.com/photos/themacinator/3445776069/
     Bike - Pauline Mak
    http://www.flickr.com/photos/__my__photos/6399028713/
     Fun - Justin Beckley
    http://www.flickr.com/photos/justinbeckleyphotography/8452437969/
     Logos used are the property of and may be trademarked by their
    respective organizations.
    

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80. #phpworld
    

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81. Thank You!
    Slides: http://speakerdeck.com/jrf
    Feedback: https://joind.in/14754
    Contact me: @jrf_nl
    jrf
    

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