🟦Typescript

Verifica comes with type definitions, so no additional packages are needed.

ensure()

function ensure(verificable: Verificable, predicate: Predicate<TOut>): TOut

Function ensure returns the checked value if the predicate matches. The type of returned value is the same as the generic parameter type of the Predicate<TOut> . This allows to use the value with the correct type after ensuring it matches the predicate:

import { asVerificable, ensure, isNumber } from "verifica";

function add(a: unknown, b: unknown): number {
    const vparams = asVerificable({ a, b });
    
    // both `aNum` and `bNum` will be of type `string`:
    const aNum = ensure(vparams.a, isNumber);
    const bNum = ensure(vparams.b, isNumber);
    
    return aNum + bNum;
}