Function: assertNonNullable()

API / @xmachines/play / assertNonNullable

function assertNonNullable<V>(value, name?): NonNullable<V>;

Defined in: packages/play/src/utils.ts:39

Asserts that value is not null and not undefined, then returns it with the type NonNullable<V>. One expression therefore holds the guard and the narrowed value.

A non-null assertion (value!) is different: it produces undefined, and your code then fails later with a message such as “undefined is not an object”. This function throws a clear error at the point of the failure.

An assertion function of the form asserts value is T is also different: this function returns the narrowed value directly. Therefore the call site needs no second variable and no as cast.

Type Parameters

Type Parameter
V

Parameters

Parameter	Type	Description
value	V	The value to check.
name?	string	The optional name in the error message. It identifies the missing value, for example the name of the variable or of the injection key.

Returns

NonNullable<V>

value with the type NonNullable<V>, without null and without undefined.

Throws

When value is null or undefined.

Example

import { assertNonNullable } from "@xmachines/play";

// inject() and assertNonNullable in one line, with no `!` and no second variable:
const actor = assertNonNullable(inject<AuthActor>("actor"), "actor");

// A lookup of an element:
const el = assertNonNullable(document.getElementById("app"), "#app");