I've come across a situation where I need to define an array of objects in TypeScript with strict typing. My current implementation looks like this:


However, the issue with the above code is that it does not provide strict type-checking for the userTestStatus object. For example, if I were to make a typo in one of the object properties, TypeScript wouldn't notify me of the error. What I want to achieve is to have TypeScript check the correctness of both the structure and the types within the userTestStatus object, and report any inconsistencies or typos. Also, I need to figure out whether it's possible to define the structure inline or if I need to create separate type definitions.
Let’s say I accidentally try to access a non-existent property like userTestStatus[3].nammme, TypeScript should flag this as an error. Could you please assist by providing the correct type definition for this case?

To solve this problem, you should define a type for the objects within your collection, and then use that type to define the structure of your userTestStatus object.
Here's an example of how you can do this:


The UserTestStatus type is an index signature that implies that every property key within the userTestStatus object must be a string, and the value must be of the type TestStatus. This way, you have strictly typed each property inside userTestStatus. Now, TypeScript will alert you if you try to access a property that does not exist or access an object property that is mistyped.

Implementing your suggestion provides a good type structure, but the types could imply that keys can be any arbitrary strings, whereas the actual keys are known and limited to "0", "1", and "2". Is there a way to restrict the keys to only those values?

Yes, you can use a Record type to map a limited set of known keys to their corresponding types like this:


Now your userTestStatus will only accept the keys "0", "1", and "2". Any attempt to use an undefined key would result in a TypeScript error.

That seems to address the constraints effectively. For completeness, here is the fully working code that ensures the correct type declaration of the userTestStatus object: