How to add featured image for category (without a plugin)?

Question

I'm finding plugins that add the option for featured images for categories, but not how to code it yourself.

Answer 1

I had missed that you can easily add fields to taxonomy terms with Advanced Custom Fields: https://www.advancedcustomfields.com/resources/get-values-from-a-taxonomy-term/

Answer 2

Not everything needs a plugin.

If you want to add a simple field to add IMG URL use add_term_meta(), the update_term_meta() and get_term_meta() WP functions.

function addTitleFieldToCat(){
    $cat_title = get_term_meta($_POST['tag_ID'], '_pagetitle', true);
    ?> 
    <tr class="form-field">
        <th scope="row" valign="top"><label for="cat_page_title"><?php _e('Category Page Title'); ?></label></th>
        <td>
        <input type="text" name="cat_title" id="cat_title" value="<?php echo $cat_title ?>"><br />
            <span class="description"><?php _e('Title for the Category '); ?></span>
        </td>
    </tr>
    <?php

}
add_action ( 'edit_category_form_fields', 'addTitleFieldToCat');

function saveCategoryFields() {
    if ( isset( $_POST['cat_title'] ) ) {
        update_term_meta($_POST['tag_ID'], '_pagetitle', $_POST['cat_title']);
    }
}
add_action ( 'edited_category', 'saveCategoryFields');

src: Luke Simmons answer from: Add custom field to Category

Answer 3

There are already some solutions out there for adding custom fields to taxonomy. See: Add custom field to Category

You will see a 2016 update near the bottom that should help you.

With this you can simply copy an image url once you have uploaded it to your Media Library but I am assuming you want an Upload Media Modal (popup window) utilizing wp.media right? You will have to do that with javascript. This post explains several methods in which to instantiate a media uploader modal: https://mikejolley.com/2012/12/21/using-the-new-wordpress-3-5-media-uploader-in-plugins/

Answer 4

<?php

add_action ( 'category_edit_form_fields', 'addTitleFieldToCat', 10, 2 );
function addTitleFieldToCat( $tag, $taxonomy ) {
    $cat_title = get_term_meta( $tag->term_id, '_pagetitle', true );
    ?>
    <tr class="form-field">
        <th scope="row" valign="top"><label for="cat_page_title"><?php _e('Category Page Title'); ?></label></th>
        <td>
            <input type="text" name="cat_title" id="cat_page_title" value="<?php echo $cat_title ?>"><br />
            <p class="description"><?php _e('Title for the category'); ?></p>
        </td>
    </tr>
    <?php
} 

add_action ( 'edited_category', 'saveCategoryFields' );
function saveCategoryFields() {
    if ( isset( $_POST['cat_title'] ) ) {
        update_term_meta( $_POST['tag_ID'], '_pagetitle', $_POST['cat_title'] );
    }
}

Code modifications suggested by user @talk-nerdy-to-me - https://wordpress.stackexchange.com/users/122776/talk-nerdy-to-me