1 00:00:00,860 --> 00:00:03,680 ‫Welcome back, now before we go deep 2 00:00:03,680 --> 00:00:06,820 ‫into actual error handling, let's first write 3 00:00:06,820 --> 00:00:09,430 ‫a handler for undefined routes. 4 00:00:09,430 --> 00:00:12,250 ‫So basically for routes that we didn't assign 5 00:00:12,250 --> 00:00:13,403 ‫any handler yet. 6 00:00:14,800 --> 00:00:17,820 ‫And first up, we need to start our application here 7 00:00:17,820 --> 00:00:21,053 ‫which we didn't quit after the recent debugging session. 8 00:00:21,950 --> 00:00:23,363 ‫So MPM start. 9 00:00:25,260 --> 00:00:28,290 ‫And so let's wait for a database connection. 10 00:00:28,290 --> 00:00:33,290 ‫Here it is, and so let's now go to Postman here 11 00:00:33,640 --> 00:00:36,810 ‫and try to hit the route that we didn't yet define. 12 00:00:36,810 --> 00:00:39,793 ‫So I'm just gonna go ahead, copy this URL here, 13 00:00:41,892 --> 00:00:44,260 ‫all right, and so for example 14 00:00:44,260 --> 00:00:46,410 ‫let's say that instead of apiV1 15 00:00:48,240 --> 00:00:49,490 ‫tours, 16 00:00:49,490 --> 00:00:53,223 ‫we would say just api/tours. 17 00:00:54,140 --> 00:00:58,400 ‫Okay so in that case we would get this HTML result, 18 00:00:58,400 --> 00:01:01,470 ‫all right, so Express automatically sends 19 00:01:01,470 --> 00:01:05,380 ‫this HTML code here, along with a 404 Not Found 20 00:01:05,380 --> 00:01:08,700 ‫error code in case that there is not any handler 21 00:01:08,700 --> 00:01:12,900 ‫for the route that was requested, okay. 22 00:01:12,900 --> 00:01:16,483 ‫Or, we could also simply misspell tour here for example. 23 00:01:17,640 --> 00:01:19,850 ‫So for example in this case we would 24 00:01:19,850 --> 00:01:21,840 ‫still get the same error. 25 00:01:21,840 --> 00:01:25,210 ‫Now there's also another situation which is if here 26 00:01:25,210 --> 00:01:29,580 ‫after tours we specify something else, 27 00:01:29,580 --> 00:01:31,800 ‫let's say just something like this. 28 00:01:31,800 --> 00:01:34,790 ‫And so let's take a look at the error that we get, 29 00:01:34,790 --> 00:01:38,470 ‫and so now we get that the cast to object ID failed. 30 00:01:38,470 --> 00:01:40,560 ‫And that's because we actually have a route that 31 00:01:40,560 --> 00:01:45,390 ‫accepts an ID parameter here after the tour/, right. 32 00:01:45,390 --> 00:01:48,770 ‫And so MongoDB is basically trying to find a document 33 00:01:48,770 --> 00:01:53,180 ‫with this ID, but cannot convert it to a valid MongoDB 34 00:01:53,180 --> 00:01:55,160 ‫object ID, all right. 35 00:01:55,160 --> 00:01:58,810 ‫So again that is a different situation, let's just 36 00:01:59,820 --> 00:02:02,930 ‫keep working with this one, so again, where we get 37 00:02:02,930 --> 00:02:05,550 ‫this error but in this HTML form. 38 00:02:05,550 --> 00:02:08,330 ‫Now since we're doing an API here, it doesn't make 39 00:02:08,330 --> 00:02:12,070 ‫much sense to send back HTML, right, and so let's 40 00:02:12,070 --> 00:02:15,400 ‫now fix this and basically create a handle function 41 00:02:15,400 --> 00:02:19,270 ‫for all the routes that are not cached by our routers. 42 00:02:19,270 --> 00:02:22,610 ‫Okay, so let's go back to our application here 43 00:02:22,610 --> 00:02:25,540 ‫and open up app.js. 44 00:02:25,540 --> 00:02:27,950 ‫Okay, so that's basically the definition 45 00:02:27,950 --> 00:02:30,180 ‫of our Express application. 46 00:02:30,180 --> 00:02:32,530 ‫Now before doing anything else 47 00:02:32,530 --> 00:02:35,190 ‫let's actually get rid of this middleware here 48 00:02:35,190 --> 00:02:36,700 ‫that we do no longer need. 49 00:02:36,700 --> 00:02:39,360 ‫So we just used this here in order to demonstrate 50 00:02:39,360 --> 00:02:43,160 ‫the concept of middleware, and so at this point 51 00:02:43,160 --> 00:02:45,080 ‫we no longer need that. 52 00:02:45,080 --> 00:02:47,980 ‫All right now how are we gonna implement a route 53 00:02:47,980 --> 00:02:51,410 ‫handler for a route that was not cached by any 54 00:02:51,410 --> 00:02:53,380 ‫of our other route handlers? 55 00:02:53,380 --> 00:02:56,160 ‫So for doing that remember that all these middleware 56 00:02:56,160 --> 00:02:59,770 ‫functions are executed in the order they are in the code. 57 00:02:59,770 --> 00:03:02,930 ‫And so the idea is that if we have a request 58 00:03:02,930 --> 00:03:06,210 ‫that makes it into this point here of our code 59 00:03:06,210 --> 00:03:08,760 ‫then it means that neither the tourRouter 60 00:03:08,760 --> 00:03:12,860 ‫nor the userRouter were able to cache it, okay. 61 00:03:12,860 --> 00:03:16,590 ‫And so if we add a middleware here after these routers 62 00:03:16,590 --> 00:03:20,060 ‫it will only be reached again if not handled by any 63 00:03:20,060 --> 00:03:22,470 ‫of our other routers, okay. 64 00:03:22,470 --> 00:03:25,610 ‫So let's do that, and then really understand how it works 65 00:03:25,610 --> 00:03:27,550 ‫after it's already implemented. 66 00:03:27,550 --> 00:03:29,600 ‫So we're gonna implement a route handler, 67 00:03:29,600 --> 00:03:30,923 ‫and so we say app. 68 00:03:32,450 --> 00:03:34,540 ‫and now the HTTP method for which 69 00:03:34,540 --> 00:03:36,380 ‫we want to specify the route. 70 00:03:36,380 --> 00:03:40,630 ‫Now we could use get here right, so just like we did before 71 00:03:40,630 --> 00:03:43,410 ‫but then what about post requests, or delete, 72 00:03:43,410 --> 00:03:45,030 ‫or patch requests? 73 00:03:45,030 --> 00:03:47,730 ‫You would then have to write handlers for these as well, 74 00:03:47,730 --> 00:03:50,190 ‫and we don't want that, we simply want to handle 75 00:03:50,190 --> 00:03:54,270 ‫all the routes, so all the URL's, for all the verbs 76 00:03:54,270 --> 00:03:56,707 ‫right here in this one handler, okay. 77 00:03:56,707 --> 00:03:59,710 ‫And so in Express, we can use app.all. 78 00:03:59,710 --> 00:04:02,460 ‫And so that's then going to run for all the verbs, 79 00:04:02,460 --> 00:04:05,430 ‫So all the HTTP method, all right. 80 00:04:05,430 --> 00:04:08,270 ‫Next up we specify the URL, and since here 81 00:04:08,270 --> 00:04:10,920 ‫we want to handle all the URL's that were not handled 82 00:04:10,920 --> 00:04:13,950 ‫before we can use the star here, which is going 83 00:04:13,950 --> 00:04:17,320 ‫to stand for everything, all right, and then the 84 00:04:17,320 --> 00:04:19,920 ‫rest is just a regular middleware function, 85 00:04:19,920 --> 00:04:21,183 ‫just like before. 86 00:04:23,980 --> 00:04:24,893 ‫So request, 87 00:04:26,210 --> 00:04:27,883 ‫response, and next. 88 00:04:29,270 --> 00:04:32,290 ‫Okay, and what do we want to do here? 89 00:04:32,290 --> 00:04:34,700 ‫Well we simply want to send back a response 90 00:04:34,700 --> 00:04:38,653 ‫in the JSON format, so not the HTML that we have right now. 91 00:04:40,100 --> 00:04:41,573 ‫So res.status, 92 00:04:43,100 --> 00:04:46,110 ‫and here let's set a 404, so Not Found 93 00:04:48,220 --> 00:04:52,190 ‫and then a JSON response, so just like the usual one 94 00:04:52,190 --> 00:04:54,343 ‫where we set the status to fail. 95 00:04:57,090 --> 00:05:01,153 ‫So just a regular adjacent formatted response. 96 00:05:03,590 --> 00:05:05,980 ‫And then some kind of message here, and actually 97 00:05:05,980 --> 00:05:07,580 ‫let's do a template string here, 98 00:05:07,580 --> 00:05:09,790 ‫because I want to put a variable in there. 99 00:05:09,790 --> 00:05:11,370 ‫So can't, 100 00:05:11,370 --> 00:05:12,203 ‫find. 101 00:05:13,380 --> 00:05:16,650 ‫And then we can use req.originalUrl 102 00:05:18,220 --> 00:05:21,900 ‫okay, so that's a property that we have on the request 103 00:05:21,900 --> 00:05:26,233 ‫which is as the name says, the URL that was requested, 104 00:05:27,300 --> 00:05:28,270 ‫all right. 105 00:05:28,270 --> 00:05:30,610 ‫So this new response that we're going to send back now 106 00:05:30,610 --> 00:05:33,230 ‫is a lot better than the HTML that 107 00:05:33,230 --> 00:05:37,163 ‫we were receiving previously, so let's now test that out. 108 00:05:40,440 --> 00:05:44,020 ‫And indeed, now we get a JSON error message back here. 109 00:05:44,020 --> 00:05:47,970 ‫And so here we also get the URL that was requested, 110 00:05:47,970 --> 00:05:50,586 ‫and indeed it's the one that we tried to access, 111 00:05:50,586 --> 00:05:54,760 ‫but it is not available, all right, great. 112 00:05:54,760 --> 00:05:57,240 ‫Now again, why did this work? 113 00:05:57,240 --> 00:06:01,200 ‫So again the idea is that if we are able to reach 114 00:06:01,200 --> 00:06:04,120 ‫this point here then it means that the request 115 00:06:04,120 --> 00:06:06,281 ‫response cycle was not yet finished 116 00:06:06,281 --> 00:06:09,100 ‫at this point in our code, right. 117 00:06:09,100 --> 00:06:11,780 ‫Because remember that middleware is added 118 00:06:11,780 --> 00:06:14,040 ‫to the middleware stack in the order that it's 119 00:06:14,040 --> 00:06:16,010 ‫defined here in our code. 120 00:06:16,010 --> 00:06:18,810 ‫And so basically this code here runs first, 121 00:06:18,810 --> 00:06:21,840 ‫and so if the route was matched here in our tourRouter 122 00:06:21,840 --> 00:06:25,230 ‫then our request would never even reach this code, 123 00:06:25,230 --> 00:06:27,660 ‫and so then this would not get executed. 124 00:06:27,660 --> 00:06:30,050 ‫And so this should basically be the last part 125 00:06:30,050 --> 00:06:32,560 ‫after all our other routes, all right. 126 00:06:32,560 --> 00:06:35,240 ‫And if I were, just to try this out, 127 00:06:35,240 --> 00:06:38,140 ‫now put this right at the top of our application 128 00:06:39,230 --> 00:06:43,260 ‫then you will see that no matter what request 129 00:06:43,260 --> 00:06:47,750 ‫we're gonna do, we will always get this same response. 130 00:06:47,750 --> 00:06:49,653 ‫Right, so let's test that, 131 00:06:51,550 --> 00:06:54,600 ‫and indeed now we get JS error message, 132 00:06:54,600 --> 00:06:56,600 ‫and so that's because all request 133 00:06:56,600 --> 00:06:59,850 ‫now reach this route handler here, and it's actually matched 134 00:06:59,850 --> 00:07:04,290 ‫because it's a GET request, which is part of all the verbs, 135 00:07:04,290 --> 00:07:08,060 ‫right, and then all of the routes, so all of the URL's 136 00:07:08,060 --> 00:07:10,760 ‫are cached here, and so of course it handles 137 00:07:10,760 --> 00:07:13,920 ‫that URL that we just did here. 138 00:07:13,920 --> 00:07:17,333 ‫And the same of course, for example for a delete tour. 139 00:07:18,330 --> 00:07:20,590 ‫So the same thing would happen we would always 140 00:07:20,590 --> 00:07:22,573 ‫get the same response, 141 00:07:23,740 --> 00:07:24,573 ‫all right. 142 00:07:25,430 --> 00:07:28,500 ‫So let's of course put it back, but this was 143 00:07:28,500 --> 00:07:33,183 ‫just to demonstrate how and why this works, 144 00:07:34,100 --> 00:07:35,670 ‫all right. 145 00:07:35,670 --> 00:07:38,890 ‫Great so this an important part to make our API 146 00:07:38,890 --> 00:07:42,150 ‫a bit more user friendly, but next up let's now 147 00:07:42,150 --> 00:07:44,873 ‫start learning about real error handling.