assert

This library is used with TypeScript support in production code where you want to reduce/infer type of certain variables.

Here is one good example:

``typescript
type User = { userId: string }

// Assume that we have getUser() that returns either null or an User object
funtion getUser(): null | User {
}

// When we know that getUser() will certainly not return null beyond this point,
// use assertExists to reduce the type to User.
const { userId } = assertExists(getUser())
`

$3


| Method | Explanation |
| --- | --- |
| `assertExists`| Assert that variable should not be neither null nor undefined.
| `assertType`| Assert the type of variable using a typeguard function.
| `assertRequired`| Assert variable to follow a certain Joi schema whose properties are required unless stated otherwise.
| `assertOptional``| Assert variable to follow a certain Joi schema whose properties are optional unless stated otherwise.