Type Inference

You rarely need to annotate everything. TypeScript infers types from values: let stars = 100 is a number with no annotation at all, and a function's return type is inferred from what it returns. Once a variable's type is inferred it is fixed, so assigning text to stars later is an error. Annotate function parameters (they cannot be inferred) and places where you want to state your intent.

How it reads

• stars is inferred as number from its first value
• double has no return annotation, but TypeScript knows it returns a number
• Parameters like n still need an annotation

Cloud tip: Let inference handle local variables, and annotate the edges: parameters and public function return types.