Tag: assertion

Jul 3, 2024 · hands on

Fixing TypeScript Error: Type undefined is not assignable to type string

Running into the TypeScript error "Type undefined is not assignable to type string"? It's a frequent error when variables might be undefined but functions demand strings. Fix it with string concatenation, templates, or assertion functions.

Jan 21, 2023 · best practices

Type Checking with Assertion Functions in TypeScript

An assertion function is a runtime check that identifies the type of unknown input. TypeScript's compiler assumes the input is of the type claimed by the assertion function's signature. Assertion functions are useful for uncertain values, like user input, and generate runtime checks. They can raise errors if the input doesn't meet criteria.