The easiest way would be to add
<input type="submit" name="update_cart" value="Update Cart" /> to your template and then add a bit of jQuery to bind the update link to the newly created update button (which you would want to hide to keep your current design).
As long as your submit button isn't called
commit (both of which submit the order),
empty_cart (which empties the cart) or
next (which updates the cart and redirects the customer to the url specified in your
next_url parameter), Store will simply update the cart quantities and redirect you to the current page.
This allows you to have both "Continue to Checkout" and "Update Totals" buttons on the same form, which both update the cart but redirect the customer to different locations. This can be seen in the
checkout.html example template which ships with Store:
<div class="form-actions"> <input type="submit" name="update_cart" value="Update Totals" class="btn" /> <input type="submit" name="empty_cart" value="Empty Cart" class="btn btn-danger" /> <input type="submit" name="next" value="Continue to Billing Details" class="btn btn-primary" /> </div>
That did it. I see the docs for update_cart, but they were not near the Updating Quantities section, which could benefit from just adding the update_cart button to the example code hint hint Adrian. Thanks Justin! Jan 30, 2013 at 19:31
To clarify, as long as your submit button isn't called
next, it will update the cart and return you to the current page (so
update_cartworks, but it doesn't actually need to be called that). I'll try to improve the documentation. Did you take a look at the sample templates? Jan 31, 2013 at 3:57
I've edited Justin's answer to clarify the options you have for updating/submitting the cart. Jan 31, 2013 at 4:05