How to secure the JavaScript API Access Token?

Question

There are numerous online resources which provide JavaScript APIs to access their services. To be more clear, I will base my question on the example of MapBox, but this appl

Answer 1

5 years later, this is not necessarily for the original poster but for anyone still interested, Mapbox now allows you to easily restrict tokens by domain(s):

https://account.mapbox.com/access-tokens (assuming you are signed in)