Learn TypeScript 3 by Building Web Applications

Use cases

There are actually quite a few valid use cases to consider for runtime type checks.

For instance, when the service layer of our WorldExplorer application makes calls to the REST API, it will get the data back as JSON. Once we get hold of the corresponding JSON, we will need to extract information from it in order to create instances of our own domain model types. Doing so requires attention to avoid runtime type safety issues.

One problem with web APIs is that their implementation can change over time. At some point, some fields that we expect to be present might be renamed or even disappear. APIs should, of course, be versioned, but theory and reality don't always agree. In addition, we might also make spelling mistakes on our ...