Add image to category screen.

functions.php

// Made by Isaac: https://gist.github.com/itzikbenh/16326bc3947f272cd6bb44de03c4774b?fref=gc&dti=168889943173228 
// and improved by Ian. https://www.facebook.com/groups/advancedwp/permalink/1607185879343620/

function add_category_meta_fields( $taxonomy ) {
    ?>
    <div class="form-field create-cat term-featured-image-wrap">
        <label for="tax-featured-image">Featured Image</label>
        <input id="tax-featured-image" type="text" name="featured_image">
        <br>
        <button id="add-cat-featured-img" class="button" name="button">Add Featured Image</button>
    </div>
    <?php
}
add_action( 'category_add_form_fields', 'add_category_meta_fields', 10 , 2 );

//This will be used both on creating and updating the category.
//It will work since update_term_meta adds if a term doesn't exist.
function update_category_meta( $term_id, $tt_id ) {
    if ( isset( $_POST['featured_image'] ) ) {
        $featured_image = sanitize_text_field( trim( $_POST['featured_image'] ) );
        update_term_meta( $term_id, 'featured_image', $featured_image );
    }
}
add_action( 'edited_category', 'update_category_meta', 10, 2 );
add_action( 'created_category', 'update_category_meta', 10, 2 );


function edit_category_meta_fields( $term, $taxonomy ) {
    $featured_image = get_term_meta( $term->term_id, 'featured_image', true );
    ?>
    <tr class="form-field term-featured-image-group">
        <th scope="row">
            <label for="featured-image">Featured Image</label>
        </th>
        <td>
        
<img src="<?php echo $featured_image; ?>" alt="" class="tax-featured-image <?php echo $featured_image ? '' : 'hidden'; ?> ">
            <input id="tax-featured-image" type="hidden" name="featured_image" value="<?php echo $featured_image; ?>">
            <?php if ( $featured_image ): ?>
                <button id="update-cat-featured-img" class="button" name="button">Update Featured Image</button>
                <button id="remove-cat-featured-img" class="button" name="button">Remove Featured Image</button>
            <?php else: ?>
                <button id="update-cat-featured-img" class="button" name="button">Add Featured Image</button>

            <?php endif; ?>
        </td>
    </tr>
    <?php
}
add_action( 'category_edit_form_fields', 'edit_category_meta_fields', 10, 2 );


function update_script() { ?>
   <script>
  jQuery('#update-cat-featured-img, #add-cat-featured-img').click(function(e) {
      e.preventDefault();

      var custom_uploader = wp.media({
          title: 'Featured Image',
          button: {
              text: 'Insert image'
          },
          multiple: false  // Set this to "add" to allow multiple files to be selected
      })
      .on('select', function() {
          var attachment = custom_uploader.state().get('selection').first().toJSON();
          jQuery('.tax-featured-image').attr('src', attachment.sizes.thumbnail.url).show();
          jQuery('#tax-featured-image').val(attachment.url);
       
      })
      .open();
  });
  jQuery('#remove-cat-featured-img').click(function(e) {
        e.preventDefault();

        jQuery('.tax-featured-image').attr('src', '');
        jQuery('#tax-featured-image').val('noimage');

  });
  </script>
<?php }
add_action( 'admin_footer',  'update_script' );