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Learning TypeScript's Functions chapter shows how a function's parameters and return types can be inferred or explicitly declared in TypeScript:

  • Declaring function parameter types with type annotations
  • Declaring optional parameters, default values, and rest parameters to change type system behavior
  • Declaring function return types with type annotations
  • Describing functions that don't return a usable value with the void type
  • Describing functions that don't return at all with the never type
  • Declaring function types in type annotations
  • Using function overloads to describe varying function call signatures