How to add shipment classes fields to WooCommerce

extend-woo-shipment-classes.php

<?php
/**
 * Extend WooCommerce Shipping Classes
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

class WC_Extend_Shippig_Classes {
    /**
     * Construct
     */
    public function __construct() {
        // WooCommerce since 2.6
        add_filter( 'woocommerce_shipping_classes_columns', array( $this, 'add_shipping_class_columns' ) );
        add_action( 'woocommerce_shipping_classes_column_extension-parcel-myvalue', array( $this, 'add_shipping_class_row_myvalue' ) );

        add_action( 'woocommerce_shipping_classes_save_class', array( $this, 'save_class' ), 10, 2 );
        add_filter( 'woocommerce_get_shipping_classes', array( $this, 'extend_terms' ), 10, 1 );

        // WooCommerce until 2.5
        add_action( 'product_shipping_class_edit_form_fields', array( $this, 'shipping_class_edit_form_fields' ), 10, 2 );
        add_action( 'edited_product_shipping_class', array( $this, 'shipping_class_edit_form_fields_save' ), 10, 1 );

        add_action( 'product_shipping_class_add_form_fields', array( $this, 'shipping_class_add_form_fields' ), 10, 1 );
        add_action( 'create_product_shipping_class', array( $this, 'shipping_class_edit_form_fields_save' ), 10, 1 );
    }

    /**
     * Adding extension columns to shipping classes (since WooCommerce 2.6)
     *
     * @param $columns
     *
     * @return array
     */
    public function add_shipping_class_columns( $columns ) {
        $extension_columns = array(
            'extension-parcel-myvalue' => __( 'My Value', 'woocommerce-extension' ),
        );

        $columns = array_merge( $columns, $extension_columns );

        return $columns;
    }

    /**
     * Adding field for myvalue (since WooCommerce 2.6)
     */
    public function add_shipping_class_row_myvalue() {
        ?>
        <div class="view">{{ data.myvalue }}</div>
        <div class="edit"><input type="text" name="myvalue[{{ data.term_id }}]" data-attribute="myvalue"  alue="{{ data.myvalue }}" placeholder="<?php esc_attr_e( '0', 'woocommerce' ); ?>"/>
        </div>
        <?php
    }

    /**
     * Saving class data (since WooCommerce 2.6)
     *
     * @param $term_id
     * @param $data
     */
    public function save_class( $term_id, $data ) {
        if ( isset( $data[ 'myvalue' ] ) ) {
            $parcel_myvalue = wc_clean( $data[ 'myvalue' ] );
        }

        update_option( 'shipping_class_' . $term_id . '_extension_myvalue', $parcel_myvalue );
    }

    /**
     * Extending terms with data from extension fields (since WooCommerce 2.6)
     *
     * @param WP_Term[] $shipping_classes
     *
     * @return WP_Term[] $shipping_classes
     */
    public function extend_terms( $shipping_classes ) {
        foreach ( $shipping_classes AS $key => $shipping_class ) {
            $term_id = $shipping_class->term_id;
            $shipping_classes[ $key ]->myvalue = get_option( 'shipping_class_' . $term_id . '_extension_myvalue' );
        }

        return $shipping_classes;
    }

    /**
     * Selecting Parcel for shipping class on editing Shipment Class (until WooCommerce 2.5)
     *
     * @param $tag
     * @param $taxonomy
     */
    public function shipping_class_edit_form_fields( $tag, $taxonomy ) {
        $term_id = $_GET[ 'tag_ID' ]; // $tag doesn't work really, so use $_GET[ 'tag_ID' ]

        $myvalue = get_option( 'shipping_class_' . $term_id . '_extension_myvalue' );

        $html = '<tr class="form-field extension-parcel-form-field">';
        $html .= '<th scope="row" colspan="2">';
        $html .= '<h3>' . __( 'My Settings', 'woocommerce-extension' ) . '</h3>';
        $html .= '</th>';
        $html .= '</tr>';

        $html .= '<tr class="form-field extension-parcel-form-field">';
        $html .= '<th scope="row">';
        $html .= '<label for="extension_parcel_myvalue">' . __( 'My Value', 'woocommerce-extension' ) . '</label>';
        $html .= '</th>';
        $html .= '<td>';
        $html .= '<input type="text" name="extension_parcel_myvalue" value="' . $myvalue . '" /> ';
        $html .= '</td>';
        $html .= '</tr>';

        echo $html;
    }

    /**
     * Selecting Parcel for shipping class on adding Shipment Class (until WooCommerce 2.5)
     */
    public function shipping_class_add_form_fields() {
        $html = '<h4>' . __( 'Shipment Settings', 'woocommerce-extension' ) . '</h4>';
        $html .= '<div class="form-field shipment-settings">';
        $html .= '<label for="extension_parcel_myvalue">' . __( 'My Value', 'woocommerce-extension' ) . '</label>';
        $html .= '<input type="text" name="extension_parcel_myvalue" />';
        $html .= '</div>';
        echo $html;
    }

    /**
     * Saving Shipping Class data on editing Shipment Class (until WooCommerce 2.5)
     *
     * @param int $term_id Term ID
     */
    public function shipping_class_edit_form_fields_save( $term_id ) {
        $parcel_myvalue = $_POST[ 'extension_parcel_myvalue' ];
        update_option( 'shipping_class_' . $term_id . '_extension_myvalue', $parcel_myvalue );
    }
}

$extend_classes = new WC_Extend_Shippig_Classes();

hey,
I am unable to understand what "{{ data.myvalue }}" this is doing
in the line

{{ data.myvalue }}

is it javascript ( or html)

I will be thankful to you if you can explain it to me

My Email-id: [email protected]