Add a custom product calculated price to Woocommerce cart

Question

In woocommerce I have added an extra text field before add to cart button to add custom charge on product purchase.

This plugin will add extra text field to single p

Answer 1

You don't need any javascript or sessions to achieve that. Try the following revisited code instead:

// Add a custom field before single add to cart
add_action( 'woocommerce_before_add_to_cart_button', 'custom_product_price_field', 5 );
function custom_product_price_field(){
    echo '<div class="custom-text text">
    <p>Extra Charge ('.get_woocommerce_currency_symbol().'):</p>
    <input type="text" name="custom_price" value="" placeholder="e.g. 10" title="Custom Text" class="custom_price text_custom text">
    </div>';
}

// Get custom field value, calculate new item price, save it as custom cart item data
add_filter('woocommerce_add_cart_item_data', 'add_custom_field_data', 20, 2 );
function add_custom_field_data( $cart_item_data, $product_id ){
    if (! isset($_POST['custom_price']))
        return $cart_item_data;

    $custom_price = (float) sanitize_text_field( $_POST['custom_price'] );
    if( empty($custom_price) )
        return $cart_item_data;

    $product    = wc_get_product($product_id); // The WC_Product Object
    $base_price = (float) $product->get_regular_price(); // Product reg price

    // New price calculation
    $new_price = $base_price + $custom_price;

    // Set the custom amount in cart object
    $cart_item_data['custom_data']['extra_charge'] = (float) $custom_price;
    $cart_item_data['custom_data']['new_price'] = (float) $new_price;
    $cart_item_data['custom_data']['unique_key'] = md5( microtime() . rand() ); // Make each item unique

    return $cart_item_data;
}

// Set the new calculated cart item price
add_action( 'woocommerce_before_calculate_totals', 'extra_price_add_custom_price', 20, 1 );
function extra_price_add_custom_price( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 )
        return;

    foreach ( $cart->get_cart() as $cart_item ) {
        if( isset($cart_item['custom_data']['new_price']) )
            $cart_item['data']->set_price( (float) $cart_item['custom_data']['new_price'] );
    }
}

// Display cart item custom price details
add_filter('woocommerce_cart_item_price', 'display_cart_items_custom_price_details', 20, 3 );
function display_cart_items_custom_price_details( $product_price, $cart_item, $cart_item_key ){
    if( isset($cart_item['custom_data']['extra_charge']) ) {
        $product = $cart_item['data'];
        $product_price  = wc_price( wc_get_price_to_display( $product, array( 'price' => $product->get_regular_price() ) ) );
        $product_price .= '<br>' . wc_price( $cart_item['custom_data']['extra_charge'] ).'&nbsp;';
        $product_price .= __("Extra Charge", "woocommerce" );
    }
    return $product_price;
}

Code goes in function.php file of your active child theme (or active theme). Tested and works.