Cart.jsx

import { Dialog, Transition } from "@headlessui/react";
import { XIcon, ShoppingCartIcon } from "@heroicons/react/outline";
import React, { Fragment } from "react";
import { useEffect } from "react";

export default function Cart({ open, setOpen, cart, updateCart}) {
  
  useEffect(() => {
    let item =  JSON.parse(localStorage.getItem('items'))
    if(item){
      updateCart(item)
    }
  },[]); // render only once when session refreshed

  useEffect(()=> {
    let item = [...cart];
    localStorage.setItem('items', JSON.stringify(item));
  },[cart]); // localStorage updated on every change on cart array.

  return (
    <Transition.Root show={open} as={Fragment}>
      <Dialog
        as="div"
        className="fixed inset-0 overflow-hidden z-10"
        onClose={() => {
          setOpen(false); // closing the cart div on backdropClick
        }}
      >
        <div className="absolute inset-0 overflow-hidden">
          <Transition.Child
            as={Fragment}
            enter="ease-in-out duration-500"
            enterFrom="opacity-0"
            enterTo="opacity-100"
            leave="ease-in-out duration-500"
            leaveFrom="opacity-100"
            leaveTo="opacity-0"
          >
            <Dialog.Overlay className="absolute inset-0 bg-gray-500 bg-opacity-75 transition-opacity" />
          </Transition.Child>

          <div className="pointer-events-none fixed inset-y-0 right-0 flex max-w-full pl-10">
            <Transition.Child
              as={Fragment}
              enter="transform transition ease-in-out duration-500 sm:duration-700"
              enterFrom="translate-x-full"
              enterTo="translate-x-0"
              leave="transform transition ease-in-out duration-500 sm:duration-700"
              leaveFrom="translate-x-0"
              leaveTo="translate-x-full"
            >
              <div className="pointer-events-auto w-screen max-w-md">
                <div className="flex h-full flex-col overflow-y-scroll bg-white shadow-xl">
                  <div className="flex-1 overflow-y-auto py-6 px-4 sm:px-6">
                    <div className="flex items-start justify-between">
                      <Dialog.Title className="text-lg font-medium text-gray-900"> Shopping cart </Dialog.Title>
                      <div className="ml-3 flex h-7 items-center">
                        <button
                          type="button"
                          className="-m-2 p-2 text-gray-400 hover:text-gray-500"
                          onClick={() => setOpen(false)}
                        >
                          <span className="sr-only">Close panel</span>
                          <XIcon className="h-6 w-6" aria-hidden="true" />
                        </button>
                      </div>
                    </div>

                    <div className="mt-8">
                      <div className="flow-root">
                        <ul role="list" className="-my-6 divide-y divide-gray-200">
                          {cart.length == 0 &&
                            <div className="flex flex-column justify-center items-center h-[20rem]">
                              <div className="items-center">
                                <ShoppingCartIcon className="flex flex-row w-12 mx-10" />
                                <div className="pt-2">Your Cart is Empty</div>
                              </div>
                            </div>}
                          {cart.map((product) => (
                            <li key={product.id} className="flex py-6">
                              <div className="h-24 w-24 flex-shrink-0 overflow-hidden rounded-md border border-gray-200">
                                <img
                                  src={product.imageSrc}
                                  alt={product.imageAlt}
                                  className="h-full w-full object-cover object-center"
                                />
                              </div>

                              <div className="ml-4 flex flex-1 flex-col">
                                <div>
                                  <div className="flex justify-between text-base font-medium text-gray-900">
                                    <h3>{product.name}</h3>
                                    <p className="ml-4">${product.price}</p>
                                  </div>
                                </div>
                                <div className="flex flex-1 items-end justify-between text-sm">
                                  <p className="text-gray-500">Qty {product.quantity}</p>

                                  <div className="flex">
                                    <button
                                      onClick={() => {
                                        let newCart = cart.filter((p) => {
                                          if (p.id === product.id) {
                                            p.quantity -= 1;
                                          }

                                          return p.quantity > 0;
                                        });
                                        updateCart(newCart);
                                      }}
                                      type="button"
                                      className="font-medium text-gray-500 hover:text-black"
                                    >
                                      Remove
                                    </button>
                                  </div>
                                </div>
                              </div>
                            </li>
                          ))}
                        </ul>
                      </div>
                    </div>
                  </div>

                  <div className="border-t border-gray-200 py-6 px-4 sm:px-6">
                    <div className="flex justify-between text-base font-medium text-gray-900">
                      <p>Subtotal</p>
                      <p>{cart.reduce((acc, prod) => {return acc + prod.price*prod.quantity},0)}</p>
                    </div>
                    <p className="mt-0.5 text-sm text-gray-500">Shipping and taxes calculated at checkout.</p>
                    <div className="mt-6">
                      <a
                        href="#"
                        className="flex items-center justify-center rounded-md border border-transparent bg-gray-800 px-6 py-3 text-base font-medium text-white shadow-sm hover:bg-black"
                      >
                        Checkout
                      </a>
                    </div>
                    <div className="mt-6 flex justify-center text-center text-sm text-gray-500">
                      <p>
                        or{" "}
                        <button
                          type="button"
                          className="font-medium text-gray-700 hover:text-black"
                          onClick={() => setOpen(false)}
                        >
                          Continue Shopping<span aria-hidden="true"> &rarr;</span>
                        </button>
                      </p>
                    </div>
                  </div>
                </div>
              </div>
            </Transition.Child>
          </div>
        </div>
      </Dialog>
    </Transition.Root>
  );
}