A collection of commonly-used assertion functions
npm install @jclem/assertProvides a set of TypeScript-friendly functions for asserting values and types
of values.
``shell`
bun add @jclem/assert
This package works by making assertions about a value, and then _returning_ the
value. This means that it works differently from other type assertions in
TypeScript such as asserts value is Type or value is Type. In order to make
use of the type-constrained value, you must use the returned value.
`typescript
import {
assert,
assertString,
assertType,
assertInstance,
} from "@jclem/assert";
class Foo {
name = "foo";
}
function maybeValue
return Math.random() > 0.5 ? value : null;
}
// Assert that a value is non-null and is defined.
const value = assert(maybeValue("Hello"));
value.length; // => 5
// Note that the returned value must be used.
const maybeString = maybeValue("Hello");
const definitelyString = assert(maybeString);
definitelyString.length; // => 5
// @ts-expect-error
maybeString.length; // => Error: Object is possibly 'null'.
// Assert that a value is a string
const str = assertString(maybeValue("Hello"));
str.length; // => 5
// Assert that a value is of a specific type
const bigint = assertType(maybeValue(1n), "bigint");
bigint.length; // => 1n
// Assert that a value is an instance of a class
const foo = assertInstance(maybeValue(new Foo()), Foo);
foo.name; // => 'foo'
``