Magento 2 - How to add product's custom attribute to checkout summary

1. Registration.php : app/code/Store/Flavor/registration.php
2. di.xml : app/code/Store/Flavor/etc/di.xml
3. module.xml : app/code/Store/Flavor/etc/module.xml
4. ConfigProviderPlugin.php : app/code/Store/Flavor/Plugin/ConfigProviderPlugin.php
5. details.js : copy of vendor/magento/module-checkout/view/frontend/web/js/view/summary/item/details.js
6. details.html : copy of vendor/magento/module-checkout/view/frontend/web/template/summary/item/details.html

<?php

\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::MODULE,
'Store_Flavor',
__DIR__
);

di.xml

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<type name="Magento\Checkout\Model\DefaultConfigProvider">
<plugin name="AddAttPlug" type="Store\Flavor\Plugin\ConfigProviderPlugin" />
</type>
</config>

module.xml

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
<module name="Store_Flavor" setup_version="1.0.0">
</module>
</config>

ConfigProviderPlugin.php

<?php

namespace Store\Flavor\Plugin;

use Magento\Checkout\Model\Session as CheckoutSession;
use Magento\Quote\Api\CartItemRepositoryInterface as QuoteItemRepository;

class ConfigProviderPlugin extends \Magento\Framework\Model\AbstractModel
{
private $checkoutSession;
private $quoteItemRepository;
protected $scopeConfig;

public function __construct(
CheckoutSession $checkoutSession,
QuoteItemRepository $quoteItemRepository,
\Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
) {
$this->_scopeConfig = $scopeConfig;
$this->checkoutSession = $checkoutSession;
$this->quoteItemRepository = $quoteItemRepository;
}

public function afterGetConfig(\Magento\Checkout\Model\DefaultConfigProvider $subject, array $result)
{
$quoteId = $this->checkoutSession->getQuote()->getId();
if ($quoteId) {
$itemOptionCount = count($result['totalsData']['items']);
$quoteItems = $this->quoteItemRepository->getList($quoteId);
$isbnOptions = array();
foreach ($quoteItems as $index => $quoteItem) {
$quoteItemId = $quoteItem['item_id'];
$isbnOptions[$quoteItemId] = $quoteItem['isbn'];
}

for ($i=0; $i < $itemOptionCount; $i++) {
$quoteParentId = $result['totalsData']['items'][$i]['item_id'];
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$productId = $result['quoteItemData'][$i]['product']['entity_id'];
$productObj = $objectManager->create('\Magento\Catalog\Model\Product')->load($productId);

$productFlavours = $productObj->getResource()->getAttribute('flavors')->getFrontend()->getValue($productObj);
if($productFlavours == 'No' || $productFlavours == 'NA'){
$productFlavours = '';
}
$result['quoteItemData'][$i]['flavor'] = $productFlavours;
json_encode($result);
}
}
return $result;
}

}

details.js

define(
[
'uiComponent'
],
function (Component) {
"use strict";
var quoteItemData = window.checkoutConfig.quoteItemData;
return Component.extend({
defaults: {
template: 'Magento_Checkout/summary/item/details'
},
quoteItemData: quoteItemData,
getValue: function(quoteItem) {
return quoteItem.name;
},
getItemFlavor: function(quoteItem) {
var itemProduct = this.getItemProduct(quoteItem.item_id);
return itemProduct.flavor;
},
getItemProduct: function(item_id) {
var itemElement = null;
_.each(this.quoteItemData, function(element, index) {
if (element.item_id == item_id) {
itemElement = element;
}
});
return itemElement;
}

});
}

);

details.html

Add this code
<span class="product-item-new" data-bind="text: getItemFlavor($parent)"></span>

If you have any further queries about the code, feel free to comment in the comment section below..