Can someone explain how this http status code is processed?

Question

I am wondering what ~(event.status / 100) > 3 is doing in the below code taken from here?

Is there a class of errors > 399?
Why do we need ~ here?

   @Injectable()
    export class AuthInterceptor implements HttpInterceptor {
      intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        console.info('req.headers =', req.headers, ';');
        return next.handle(req)
          .map((event: HttpEvent<any>) => {
            if (event instanceof HttpResponse && ~(event.status / 100) > 3) {
              console.info('HttpResponse::event =', event, ';');
            } else console.info('event =', event, ';');
            return event;
          })
          .catch((err: any, caught) => {
            if (err instanceof HttpErrorResponse) {
              if (err.status === 403) {
                console.info('err.error =', err.error, ';');
              }
              return Observable.throw(err);
            }
          });
      }
    }

400* errors have something to do with authroization (usually). 500* errors often have to do with application errors. Take a look of the whole list https://en.wikipedia.org/wiki/List_of_HTTP_status_codes — Candide, Oct 30 '17 at 13:13
A good read [What does a tilde do when it precedes an expression?](https://stackoverflow.com/questions/12299665/what-does-a-tilde-do-when-it-precedes-an-expression) — Satpal, Oct 30 '17 at 13:13
@epascarello the tilde `~`, what does that do? also, all codes above `3` falls to some category? — sabithpocker, Oct 30 '17 at 13:13
@ParijatPurohit I am wondering why we need a bitwise operation here? — sabithpocker, Oct 30 '17 at 13:16
@sabithpocker same is what i am wondering :P I cant find a reason to do a negation of the status code. Although `(statuscode/100) > (some number)` is kind of a standard practice. — Parijat Purohit, Oct 30 '17 at 13:18

score 3 · Answer 1 · edited Oct 30 '17 at 13:30

~ is bitwise NOT operator. MDN

~(event.status / 100) > 3 is same as event.status <= -500.
Please see below snippet.

a = 200;
console.log( ~(a / 100) , ~(a / 100) >3 );
a = 300;
console.log( ~(a / 100), ~(a / 100) >3  );
a = 400;
console.log( ~(a / 100), ~(a / 100) >3  );

a = -200;
console.log( ~(a / 100), ~(a / 100) >3  );
a = -300;
console.log( ~(a / 100), ~(a / 100) >3 );
a = -400;
console.log( ~(a / 100), ~(a / 100) >3 );
a = -500;
console.log( ~(a / 100), ~(a / 100) >3 );

score 0 · Answer 2 · answered Oct 30 '17 at 13:22

The code is determining if the HTTP response is either a information response or a successful Response. Since the information and successful responses range from the response codes 100 to 226. You can view a list of HTTP response codes at https://developer.mozilla.org/en-US/docs/Web/HTTP/Status . An HTTP response code is just telling you the current state of the connection to a URL. For example if the code is 226, it means that the web server is at the state "IM Used".

In the case of the code you showed it is logging the information and successful codes to the console while others are being let through and into the code that requires that information.

I hope that this will help you understand the functionality of the code.

Can someone explain how this http status code is processed?

2 Answers2