API Fundamentals
/Intermediate
Backward Compatibility
Definition
Designing software systems so that newer updates do not break older client applications that have not yet been updated.
Explain Like I'm New
If you buy an Xbox Series X (new), it can still play Xbox 360 games (old). That is backward compatibility. In APIs, it means you can upgrade your backend to be faster and better, but the old iPhone app from 4 years ago can still talk to it without crashing.
Real World Example
You realize `user.age` is a terrible database field because it changes every year. You update the DB to store `user.dateOfBirth`. To maintain backward compatibility, your API still calculates and returns `user.age` in the JSON response so old apps don't break, while also returning the new `dateOfBirth` field for new apps.
Common Use Cases
- •Mobile app lifecycles
- •Public API management
Interactive Example
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Interview Questions
basic
- If you add an entirely new API endpoint (like `/api/v1/analytics`), does that break backward compatibility?
intermediate
- What is an API 'Deprecation' strategy?