I am reading the Angular - Testing documentation. When describing how to test asynchronous services (Testing HTTP services) I encountered a class constructor with an <any>
in front of the passed argument. The complete line is given by
heroService = new HeroService(<any> httpClientSpy);
I know, that any
in Typescript stands for literally "any" type. What are the guillemets (<...>
) used for? And why is the typing in front of the argument? Is it used for type parsing?
The full code from the documentation:
let httpClientSpy: { get: jasmine.Spy };
let heroService: HeroService;
beforeEach(() => {
// TODO: spy on other methods too
httpClientSpy = jasmine.createSpyObj('HttpClient', ['get']);
heroService = new HeroService(<any> httpClientSpy);
});
it('should return expected heroes (HttpClient called once)', () => {
const expectedHeroes: Hero[] =
[{ id: 1, name: 'A' }, { id: 2, name: 'B' }];
httpClientSpy.get.and.returnValue(asyncData(expectedHeroes));
heroService.getHeroes().subscribe(
heroes => expect(heroes).toEqual(expectedHeroes, 'expected heroes'),
fail
);
expect(httpClientSpy.get.calls.count()).toBe(1, 'one call');
});
it('should return an error when the server returns a 404', () => {
const errorResponse = new HttpErrorResponse({
error: 'test 404 error',
status: 404, statusText: 'Not Found'
});
httpClientSpy.get.and.returnValue(asyncError(errorResponse));
heroService.getHeroes().subscribe(
heroes => fail('expected an error, not heroes'),
error => expect(error.message).toContain('test 404 error')
);
});
This is type assertion.
Originally the syntax that was added was
<foo>
. However, there is an ambiguity in the language grammar when using<foo>
style assertions in JSX. Therefore it is now recommended that you just useas foo
for consistency.
https://basarat.gitbooks.io/typescript/docs/types/type-assertion.html