This concept combines a buy button with a quantity selector, making it easy for the user to add an item to their cart and increase it's quantity without moving their mouse/focus. The middle area is a text field, so the user can manually enter the quantity if they wish.
By the way, we've been using this button for a while now at Peapod (in the mobile app), as well as on the Stop & Shop Shopping List application. You can see how we make it work here (just click the "Try It" button and then enter a NYC zip code like 10001): https://www.stopandshop.com/listmaster/user/login.htm
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