This multi-functional extension changes the cart button based on set criteria.
Product quantity is fetched in real time (AJAX) while the customer loads the page.
Optionally prevent customers from adding products to cart that are not (anymore) in stock (quantity = 0)
(read documentation for details)

Stock status to cart button with a custom color and the name of the stock status as the text.
There's a ton of other features...read on!
Features
- Real time (on page load) stock updates for all products
- (Option) Prevent adding to cart for products with zero quantity
- (Option) Automatic redirect to the checkout page after adding to cart
- (Option) Change the cart button text and/or color site wide.
- (Option) Completely hide the cart button on zero quantity.
- (Option) Automatic cart button color and text based on stock status
- All available Stock statuses are added automatically.
- (Option) Custom minimum amount triggers a quantity count down on cart button (see manual section)
- (Option) Custom popup message informs the customer after clicking add-to-cart.
More info & Buy
Online Documentation