I'm programming an online shop with HTML + JavaScript.
I have noticed that I can manipulate the price and amount of items in the shopping cart in the Chrome web browser.
My concern is, that a hacker can manipulate the shopping cart and order the stuff.
How can I make it safe? Is it safe just to run it on the clint site?
When you edit HTML code in browser by Chrome DevTools (or any similar dev tool in other browser) then you are editing this only in your side.
This is because everything that your browser is displaying was received from server (shop). Just because you changed price, does not mean that this prices was changed in server.
Imagine that someone sent you a letter saying "I like You". You took pen and changed it to "I LOVE You". Does this mean that this person now loves you? Unfortunately no... :(