This is a Next.js + Shopify Cart API demo! Check out the site here. If you want to make your own version, make sure you create a Shopify account and create some products, and install the Netlify CLI.
Once you have your shop set up, add environment variables to your setup:
SHOPIFY_STOREFRONT_API_TOKEN=example
SHOPIFY_API_ENDPOINT=https://exampleshopify/graphql.json
First, run the development server:
netlify dev
Open http://localhost:8888 with your browser to see the result.