Adding a field type

Checkoutline keeps a list of field types, and other plugins can add to it with the checkoutline_field_types filter. A new type shows up in the Type dropdown, works in both checkouts, and its answers show on orders like any other.

What a type is

Each type says how it looks in each checkout:

Key	Meaning	Default
label	The name in the Type dropdown (required)
block	The Checkout block's field type: text, select or checkbox, the only three it has	text
classic	The classic checkout's woocommerce_form_field() type, such as text, textarea, select, radio, tel, url or date	text
options	Whether the type has options (value => label), entered on the field's screen	false
placeholder	Whether the field's screen offers a placeholder	true

Checkoutline's own types (text, textarea, select, checkbox) can't be replaced.

Example: a website address

/**
 * Plugin Name: Website field for Checkoutline
 */

add_action( 'checkoutline_loaded', function () {
	// The type.
	add_filter( 'checkoutline_field_types', function ( $types ) {
		$types['website'] = array(
			'label'   => __( 'Website address', 'my-plugin' ),
			'block'   => 'text',
			'classic' => 'url',
		);
		return $types;
	} );

	// Let browsers fill it in, in the Checkout block.
	add_filter( 'checkoutline_block_field', function ( $args, $field ) {
		if ( 'website' === $field['type'] ) {
			$args['attributes'] = array( 'autocomplete' => 'url' );
		}
		return $args;
	}, 10, 2 );

	// Check it, in both checkouts.
	add_filter( 'checkoutline_value_problem', function ( $problem, $field, $value ) {
		if ( '' === $problem && 'website' === $field['type'] && ! wp_http_validate_url( $value ) ) {
			/* translators: %s: field label */
			return sprintf( __( '%s must be a web address, starting with https://.', 'my-plugin' ), $field['label'] );
		}
		return $problem;
	}, 10, 3 );
} );

Activate it, and Website address is in the Type dropdown on WooCommerce → Checkout Fields.

If your plugin is deactivated

Fields of your type are kept, with all their settings and answers, but Checkoutline leaves them out of checkout until a plugin registers the type again. The list of fields says so under the field's name. That way a field is never shown in a shape it wasn't made for.

Settings of your own

To store a setting on a field (say, a list of allowed domains for the website field), add a row to the field's screen with checkoutline_field_rows, read it in checkoutline_posted_field, and clean it in checkoutline_clean_field. See Filters and hooks.