accidental added adds behavior button buttons buyer buyers cart carts clicked clicking doesn down drop drop-down existing familiar industry item list mis-ordering nearly normally online prevents problem qty quantity re-insert remove running selects shopping site sites specified specifies standard twice universal update updated user

On my site, I have a drop down list that specifies the quantity of the item to be added to cart, but I am running into a problem: say the user selects 5 from the drop-down then adds to cart, then selects 2 and adds the same item to cart again, the existing item's quantity in cart doesn't get updated (it still shows as 5)

Is there a way to have the "add to cart" button update the quantity in cart, or remove the item and re-insert with the new quantity?

Add to Cart buttons cannot change the quantity of an item that has already been added to the cart -- e.g., even a standard Add to Cart button for a given item clicked twice would not set qty=2 for that item in the cart. Quantity is normally specified by the buyer in the cart, rather than before clicking the Add to Cart button. All of this is nearly universal "industry standard" behavior for online shopping carts, which buyers should already be familiar with from shopping on other sites. This prevents accidental mis-ordering such as when the buyer doesn't realize they'd already added an item to their cart.