Add custom fields in user registration WooCommerce

add-custom-fields-in-user-registration-woocommerce.php

<?php

/**
 * Displaying first name and last name fields on 
 * WooCommerce's registration page.
 */

function woocommerce_register_form() {
    $fields = array(
        'first_name' 	=> __('First name', 'woocommerce'),
        'last_name' 	=> __('Last name', 'woocommerce')
    );
    foreach( $fields as $k => $v ): ?>
        <p class="form-row form-row-wide">
        <label for="<?php echo $k; ?>"><?php echo $v; ?> <span class="required">*</span></label>
        <input type="text" class="input-text" name="<?php echo $k; ?>" id="<?php echo $k; ?>" value="<?php 
                if ( ! empty( $_POST[$k] ) ) echo esc_attr( $_POST[$k] ); ?>" />
        </p>
    <?php 
    endforeach;
}
add_action( 'woocommerce_register_form_start', 'woocommerce_register_form' );

/**
 * Validate the extra register fields.
 */

function woocommerce_registration_errors( $validation_error, $username, $password, $email )
{
    if( !isset($_POST['first_name']) || empty($_POST['first_name']) ){
        $validation_error->add('error', 'Please enter your First name');
    }
    elseif( !isset($_POST['last_name']) || empty($_POST['last_name']) ){
        $validation_error->add('error', 'Please enter your Last name');
    }
    return $validation_error;
}
add_filter( 'woocommerce_process_registration_errors', 'woocommerce_registration_errors', 10, 4 );

/**
 * Save the extra register fields.
 */

function woocommerce_new_customer_data( $data ) {
    /**
     * generate username from first/last name field input
     * only if username field is inactive
    **/
    if ( 'no' !== get_option( 'woocommerce_registration_generate_username' ) || ! empty( $username ) ) :
        $username = sanitize_user( wc_clean( $_POST['first_name'] ) );

        if( username_exists( $username ) ) :
            $username .= sanitize_user( wc_clean( $_POST['last_name'] ) );
        endif;

        // Ensure username is unique
        $append     = 1;
        $o_username = $username;

        while ( username_exists( $username ) ) :
            $username = $o_username . $append;
            $append ++;
        endwhile;

        $data['user_login'] = $username;

    endif;

    /**
     * WordPress will automatically insert this information's into database, 
     * we just need to include it here
    **/
    $data['first_name'] = wc_clean( $_POST['first_name'] );
    $data['last_name'] = wc_clean( $_POST['last_name'] );

    return $data;
}
add_filter( 'woocommerce_new_customer_data', 'woocommerce_new_customer_data' );