assertType ()

assertType<T>(x, guard, message?): asserts x is T
Asserts a type via a given guard.
Type Parameters
- T
Parameters
- x: unknown
- guard: ((x) => x is T)
  - - (x): x is T
    - Parameters
      x: unknown
      Returns x is T
- Optional message: string
Returns asserts x is T
Example
```
const a: unknown = 1 as unknown;
assertType(a, isNumber);
const b: number = a; // ok
```
- Defined in Opt.ts:3356
assertType<T>(x, guard, errorFactory): asserts x is T
Type Parameters
- T
Parameters
- x: unknown
- guard: ((x) => x is T)
  - - (x): x is T
    - Parameters
      x: unknown
      Returns x is T
- errorFactory: (() => unknown)
  - - (): unknown
    - Returns unknown
Returns asserts x is T
- Defined in Opt.ts:3357