APIs all the way down Frontend and backend developers these days have to deal with many external APIs, usually REST APIs. Fetching data is easy, but making sure the data is valid and conforms to an expected schema can get messy. Foreign APIs can change over time or simply deliver rubbish, especially on Friday afternoons or at midnight during a lunar eclipse. It is therefore important to detect issues quickly and reliably to prevent error propagation to the deeper parts of our software architecture.

Motivation After migrating our company homepage to Gridsome in 2019, I quickly realized how fragile refactorings could be. Renaming a field in a blog article would silently break layout of some dependent components. Regex-searches and repeated manual testing were the most used tools. This could have easily been prevented with compile-time type checking. I already had the experience from previous projects, how migrating from Javascript to Typescript boosts confidence and willingness for change.