Custom matcher for Jasmine > 2.0 to verify if a given value is an instance of the expected type

tobeinstanceof.ts

/* Run this during setup */

beforeAll(() => {
	jasmine.addMatchers({
		toBeInstanceOf: function() {
			return {
				compare: function(actual: any, expected: {new (...args: any[]): any}) {
					const pass = actual instanceof expected;
					return {
						pass,
						message: `Expected instance of ${actual.constructor.name} ${pass ? 'not ' : ''}to be an instance of ${expected.name}`,
					};
				},
			};
		},
	});
});

/* Declare the matcher so TypeScript doesn't complain */

declare module jasmine {
	interface Matchers {
		toBeInstanceOf(expected: {new (...args: any[]): any}): boolean;
	}
}