1
00:00:00,340 --> 00:00:05,510
A 404 signals that the user
requested a route that doesn't exist.

2
00:00:05,510 --> 00:00:08,670
Remember, when an app gets a request,

3
00:00:08,670 --> 00:00:12,880
it will go from one app.use call
to the next looking for a match.

4
00:00:13,880 --> 00:00:19,808
If it gets to the end without finding
a route and there are no errors,

5
00:00:19,808 --> 00:00:26,220
Express' native handler will send a 404
back to the client with some plain text.

6
00:00:26,220 --> 00:00:30,120
If we catch the request before
it gets to the end of the line,

7
00:00:30,120 --> 00:00:32,180
we can send users a better page.

8
00:00:33,540 --> 00:00:37,960
Check out Treehouse's 404 page, or Lego's,

9
00:00:39,470 --> 00:00:42,410
or my personal favorite, GitHub.

10
00:00:42,410 --> 00:00:46,130
We can give our users
a less scary page too.

11
00:00:46,130 --> 00:00:50,250
Let's write some middleware to
handle 404 errors in our app.

12
00:00:51,560 --> 00:00:58,660
We want to access the request at the end
of our app and before the error handler.

13
00:00:58,660 --> 00:01:03,104
So let's call app.use here.

14
00:01:10,033 --> 00:01:13,549
We're going to use the error
handler we wrote in the last video

15
00:01:13,549 --> 00:01:15,180
to handle the actual error.

16
00:01:16,740 --> 00:01:19,080
This middleware will
just be responsible for

17
00:01:19,080 --> 00:01:23,310
creating the error object and
handing off to the error handler.

18
00:01:25,135 --> 00:01:33,116
I'll create a new error, Not found.

19
00:01:36,770 --> 00:01:39,988
Then I'll set the error status code,

20
00:01:42,312 --> 00:01:49,025
To 404,
Before parsing it to the next function.

21
00:01:53,250 --> 00:01:58,866
Now, any requests that makes it
this far will run this function and

22
00:01:58,866 --> 00:02:01,280
trigger the error handler.

23
00:02:01,280 --> 00:02:06,430
The error handler itself will send
the page out to the user in that event.

24
00:02:06,430 --> 00:02:08,090
Let's try it out.

25
00:02:08,090 --> 00:02:10,942
In the browser,
I'll request a route that doesn't exist.

26
00:02:16,040 --> 00:02:22,427
Voila, now when our users go astray,
they will get a friendlier notice.

27
00:02:22,427 --> 00:02:25,982
We've covered the basics of Express now,
well done.

28
00:02:25,982 --> 00:02:28,922
Let's cement your knowledge in
the remainder of this course by

29
00:02:28,922 --> 00:02:30,814
finishing our flash card application.

30
00:02:30,814 --> 00:02:33,290
Are you ready to apply your knowledge?

31
00:02:33,290 --> 00:02:33,790
See you there.