PHP, MySQL, LocalStorage, Ajax

I want to make a shopping cart that stores product content in localStorage and implement Ajax (adding items to the shopping cart will not refresh the page, and adding or reducing the number of items in the shopping cart will not refresh the page). On the page, the code for adding items to the shopping cart is as follows (Im not sure whether to use a tag or button?)

What I want to ask is if I want to achieve the above description, what are my steps? For example, first obtain the corresponding product id through Ajax, then obtain the product information data from the database based on this id, and then convert PHP into JSON and forward it to JavaScript, and then store it in localStorage? Can you give me some clear ideas? Thank you.

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