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Why exceptions should not be used in this case

The problem with throwing an exception in the getNewBookCollectionName method is that it changes the control flow of the application. The calling code will have to explicitly catch this exception if it wants to be able to react to it. However, since there is no notion such as checked exceptions in JavaScript and TypeScript, the calling code might not even know that an exception could be raised when calling the method!

Note that proper code documentation and tools can help with this issue. For instance, you can add JSDoc comments to the code to explicitly state that it might throw an error: http://usejsdoc.org/tags-throws.html.

We say that throwing exceptions changes the control flow because, ...