1 00:00:02,029 --> 00:00:04,000 Now we made huge progress, 2 00:00:04,000 --> 00:00:06,100 and we get the general sign up 3 00:00:06,100 --> 00:00:09,320 and authentication flows implemented, 4 00:00:09,320 --> 00:00:11,850 still there is room for improvement. 5 00:00:11,850 --> 00:00:14,120 For example, we have no validation, 6 00:00:14,120 --> 00:00:17,040 and we show no validation errors to the user 7 00:00:17,040 --> 00:00:19,730 if we enter incorrect data here 8 00:00:19,730 --> 00:00:22,680 or if we have deviating email addresses here 9 00:00:22,680 --> 00:00:25,760 when we sign up, so that's something we wanna add. 10 00:00:25,760 --> 00:00:26,920 But before we do that, 11 00:00:26,920 --> 00:00:30,500 I wanna come back to error handling in general. 12 00:00:30,500 --> 00:00:33,100 We did add the error-handler middleware 13 00:00:33,100 --> 00:00:35,290 a couple of minutes ago. 14 00:00:35,290 --> 00:00:39,320 But this middleware, which is executed by Express 15 00:00:39,320 --> 00:00:42,173 automatically if an error occurs, has a flow. 16 00:00:43,030 --> 00:00:45,940 Yes, Express will execute it automatically 17 00:00:45,940 --> 00:00:49,330 if some error occurs in any other middleware. 18 00:00:49,330 --> 00:00:53,360 But unfortunately, Express ignores errors 19 00:00:53,360 --> 00:00:57,940 that are occurring inside of asynchronous operations. 20 00:00:57,940 --> 00:01:00,690 So if I await the user sign up here 21 00:01:00,690 --> 00:01:04,680 and inside the signup method or some other function called 22 00:01:04,680 --> 00:01:08,000 inside of the sign up method; something goes wrong, 23 00:01:08,000 --> 00:01:11,693 the Express middleware handler will not become active. 24 00:01:12,800 --> 00:01:15,260 Therefore, we have to handle this manually, 25 00:01:15,260 --> 00:01:17,030 and we learned how we can do this 26 00:01:17,030 --> 00:01:21,303 early in the course as well: with help of try catch. 27 00:01:23,270 --> 00:01:27,510 Try catch allows us to implement our own error handling, 28 00:01:27,510 --> 00:01:31,060 and it allows us to try some operation. 29 00:01:31,060 --> 00:01:35,060 And we can use try catch when we use async await 30 00:01:35,060 --> 00:01:37,970 to then catch a potential error, 31 00:01:37,970 --> 00:01:40,770 which we receive as a parameter value here, 32 00:01:40,770 --> 00:01:43,000 in case this operation 33 00:01:43,000 --> 00:01:46,663 or some nested operation in there goes wrong. 34 00:01:48,180 --> 00:01:50,370 And then here in the catch case, 35 00:01:50,370 --> 00:01:54,440 to use the default Express error handling middleware, 36 00:01:54,440 --> 00:01:56,290 what we can do is we can use 37 00:01:56,290 --> 00:02:00,010 that third parameter value, this "next" function, 38 00:02:00,010 --> 00:02:04,120 which we always get in all our middleware functions, 39 00:02:04,120 --> 00:02:07,000 and our controller actions here are 40 00:02:07,000 --> 00:02:09,270 just middleware functions in the end. 41 00:02:09,270 --> 00:02:12,363 And we can call next here in catch, 42 00:02:13,630 --> 00:02:15,580 and pass the error to it, 43 00:02:15,580 --> 00:02:18,270 and then either return this 44 00:02:18,270 --> 00:02:21,780 or return thereafter, doesn't matter. 45 00:02:21,780 --> 00:02:24,180 So that's the next line doesn't execute 46 00:02:25,270 --> 00:02:27,660 because when we pass an error to next 47 00:02:27,660 --> 00:02:30,120 and we execute next with that error, 48 00:02:30,120 --> 00:02:33,690 the default error handling middleware will become active, 49 00:02:33,690 --> 00:02:36,220 and in our case, that middleware will 50 00:02:36,220 --> 00:02:39,283 then render this 500 template. 51 00:02:40,740 --> 00:02:43,330 And then I don't wanna redirect in addition to it, 52 00:02:43,330 --> 00:02:45,400 which is why we have to return thereafter 53 00:02:45,400 --> 00:02:48,390 so that this code doesn't execute. 54 00:02:48,390 --> 00:02:51,720 But it's this kind of custom error handling logic 55 00:02:51,720 --> 00:02:53,760 that we wanna add to all the parts 56 00:02:53,760 --> 00:02:56,940 in our code that could possibly fail. 57 00:02:56,940 --> 00:03:01,710 For example, here when we get a user with the same email; 58 00:03:01,710 --> 00:03:05,120 I wanna try this: 59 00:03:05,120 --> 00:03:08,030 catch the error here 60 00:03:08,030 --> 00:03:12,343 and call next error if that fails. 61 00:03:14,830 --> 00:03:18,400 So here I call next error then if that fails, 62 00:03:18,400 --> 00:03:19,950 and then return thereafter. 63 00:03:19,950 --> 00:03:21,510 Because if that fails, 64 00:03:21,510 --> 00:03:24,623 we don't wanna execute any of our code in this action. 65 00:03:25,470 --> 00:03:28,990 And now with this approach, we just would face one problem: 66 00:03:28,990 --> 00:03:33,990 The existing user constant now is scoped to this try block. 67 00:03:34,280 --> 00:03:36,060 You'll learn about variable scoping 68 00:03:36,060 --> 00:03:37,560 before in this course as well, 69 00:03:37,560 --> 00:03:39,700 and it basically means that a variable 70 00:03:39,700 --> 00:03:43,310 or constant is only available inside of the block 71 00:03:43,310 --> 00:03:46,430 of curly braces in which it is defined; 72 00:03:46,430 --> 00:03:48,053 in this case, inside of try. 73 00:03:49,100 --> 00:03:51,670 But I wanna use existing user thereafter 74 00:03:51,670 --> 00:03:53,830 and to make it available thereafter. 75 00:03:53,830 --> 00:03:55,250 We simply have to define it 76 00:03:55,250 --> 00:03:57,650 as a variable in an outer block, 77 00:03:57,650 --> 00:04:00,120 and then assign a value in the inner block; 78 00:04:00,120 --> 00:04:02,850 that is allowed, you can access variables 79 00:04:02,850 --> 00:04:04,730 that are scoped to an outer block 80 00:04:04,730 --> 00:04:06,740 from inside the inner block; 81 00:04:06,740 --> 00:04:09,460 the other way around doesn't work though, 82 00:04:09,460 --> 00:04:11,630 which is why we can solve this problem like this, 83 00:04:11,630 --> 00:04:14,200 and then handle this potential error. 84 00:04:14,200 --> 00:04:17,913 And with that, we also improve our log in function here. 85 00:04:19,649 --> 00:04:21,760 We could add more error handling 86 00:04:21,760 --> 00:04:24,610 but comparing the password, actually shouldn't fail here. 87 00:04:24,610 --> 00:04:27,120 So therefore, that's the only error handling 88 00:04:27,120 --> 00:04:29,073 I wanna add here in this case. 89 00:04:30,370 --> 00:04:32,960 But with that, we improved our functions 90 00:04:32,960 --> 00:04:35,500 to add better error handling. 91 00:04:35,500 --> 00:04:39,760 With that done, we can now work on validating the user input 92 00:04:39,760 --> 00:04:41,850 and showing some feedback to the user. 93 00:04:41,850 --> 00:04:45,903 If, for example, different email addresses were provided.