Is TypeScript a functional programming language?

The answer to this question is yes, but only in part. TypeScript is a multi-paradigm programming language and, as a result, it includes many influences from both OOP languages and functional programming paradigms.

However, if we focus on TypeScript as a functional programming language, we can observe that it is not a purely functional programming language because, for example, the TypeScript compiler doesn't force our code to be free of side-effects.

Not being a purely functional programming language should not be interpreted as something negative. TypeScript provides us with an extensive set of features that allow us to take advantage of some of the best features of the world of OOP languages and the world of functional programming languages. This has allowed TypeScript-type systems to attain a very good compromise between productivity and formality.