as
Performs a type assertion telling the compiler to treat a value as a given type.
Syntax
expression as TargetTypeExamples
const el = document.getElementById('app') as HTMLInputElement;
el.value = 'hello';
const data = JSON.parse(raw) as { id: number };
const wide = 'on' as const; // const assertion
Notes
Assertions are compile-time only and perform no runtime check or conversion.
TypeScript only allows assertions between types with some overlap; use
`as unknown as T` to force an unrelated cast. Prefer type guards over
assertions where possible. `as const` narrows to literal readonly types.