Typescript doesn't throw error in .d.ts files

Question

I have a *.d.ts files with the following content.

declare var a: SomeType;

I have not declared a type named SomeType anywhere, still, there is no error here instead typescript automatically interprets it as any. Changing the extension of the file from *.d.ts to *.ts there is an error.

Why is that? Is there something I can do so that typescript throws errors in *.d.ts files?

Answer 1

In my case, this was happening because I had "skipLibCheck": true in my tsconfig.json. Turning it to false fixed this problem.

Answer 2

This is intentional maybe this GitHub Issue will help you to better understand why that happens