I want to pass my custom_price changed via jQuery to my Observer in Magento 2 to have the correct price in my cart.

**My /Observer/CustomPrice.php:**

    <?php
        namespace Vendor_Name\Module_Name\Observer;
     
        use Magento\Framework\Event\ObserverInterface;
        use Magento\Framework\App\RequestInterface;
     
        class CustomPrice implements ObserverInterface
        {
            public function execute(\Magento\Framework\Event\Observer $observer) {
                $item = $observer->getEvent()->getData('quote_item');         
                $item = ( $item->getParentItem() ? $item->getParentItem() : $item );
                $price = 123; // CUSTOM_PRICE variable HERE instead of "123"
                $item->setCustomPrice($price);
                $item->setOriginalCustomPrice($price);
                $item->getProduct()->setIsSuperMode(true);
            }
     
        }
    ?>

**Excerpt of my JS script /view/frontend/web/product.js:**

    require([ 'jquery'], function($){
    $(document).ready(function () {
    
    //... price calculations
    custom_price = price + product_attribute_value
    $("#custom_price").html(custom_price);
    
    };
    };

**Edit for completion: My etc/frontend/events.xml:**

    <?xml version="1.0"?>
    <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
        <event name="checkout_cart_product_add_after">
            <observer name="customprice" instance="Vendor_Name\Module_Name\Observer\CustomPrice" />
        </event>
    </config>

My question is: How to **replace** the **"123"** value within the observer with my **"custom_price"** value from the jQuery calculations? (I know this is not the safest way to build up this thing on client site, but it should be fine since every price is getting checked manually after customer checkout).

**Further comments:**

 1. The Observer is working fine with "123" 
 2. Using Magento 2.1.3

I also have a working extension for Magento 2.1 which does this without any Observer (only Controller/Cart/Add.php). I have still no clue how this is possible - trying to learn M2. After my update to 2.1.3 the functionality stopped working. An observer seems to be the right way to go for me. What do you think?

Regards,
eskaliert