Assert.instanceOf()

added in 0.5.0 • last revisions

Syntax

function instanceOf(value: unknown, constructor: Constructor, name?: string): void

Asserts that a value has a certain prototype in its prototype chain.

Parameters
`value`	The value to check.
`constructor`	Any valid constructor. Does not have to be instantiable. The function will check whether `value instanceof constructor` evaluates to `true`.
`name` Optional	A variable, property, or parameter name which, if specified, will print the name as part of the assertion error to make it more clear where the error originated.

Example

import { Assert } from 'potence';

function ensureValueIsDate(arg: unknown) {
    Assert.instanceOf(arg, Date, 'arg');
}

ensureValueIsDate(new Date());    // OK
ensureValueIsDate(new Object());  // AssertionError: "Assertion failed: expected arg to be instance of Date but was {}"

Remarks

This function is a TypeScript assertion function meaning it behaves exactly the same as if (value instanceof type) { ... }, narrowing the type to exclude null and undefined if possible.