jquery-smartcart
https://github.com/techlab/jquery-smartcart

other
https://code-boxx.com/simple-vanilla-javascript-shopping-cart/#sec-download
https://medium.com/sharing-and-learning/creating-a-shopping-cart-with-vanilla-javascript-23b2e4d8e1ef
https://codepen.io/celina-ngth/pen/wvzKJXo
https://www.cssscript.com/shopping-cart-localstorage/

ไม่เข้าใจ
https://dev.to/wenglin1/simple-shopping-cart-with-js-json-jdp

more
https://www.digitaldesignjournal.com/best-jquery-shopping-cart-plugins/