Tl;dr: I'm a shitty PHP programmer, but even a shittier JS programmer.

I made a whole image upload system which has an elaborate login/sign up facility, checks the dimensions of an image, it's size, checks if it's broken, compares it to previous uploads to prevent duplicates, take comments, sorts them per user and stores it efficiently in a db and accesses it using PDO, not mySQL, displays it as a gallery, and even lets the users transfer images amongst them.
But I can't make a simple shopping cart in js.

Why? Just, why?

Did you make the uploader from an example? Because all functions needed for a shopping cart are in the things you described you did.

Except a working order/checkout part.

A shopping list could be as easy as list with 4 properties. ItemID, name, price, amount. And the js part that can add/remove/update the list.

@aronmik Yea I can't seem to get the shopping cart working completely. I'm currently using sessions, localstorage and DOM and it's a huge mess.

@alcatraz627 you might be diving in to deep. It looks like you are trying to do things that you not fully understand yet.

I would recommend not trying to put al the new things together as a finished fancy product.

But build them apart first until you understand the every basic component. You really need to know how the basic concept work or else it would be impossible to debug your code and near to impossible to build a stable product.

I would even recommend to not copy and past code. But for every part that you copy rewrite it until you understand it. And yeah this is way slower but you gotta know how it works.