WEBVTT 00:03.790 --> 00:05.320 Hey, did everyone a day share? 00:05.320 --> 00:07.600 And welcome to another video of this section. 00:07.600 --> 00:13.210 Yes, I know we are going quite a lot in the theoretical section and this video is also kind of a mix 00:13.210 --> 00:15.040 of theory and a bit of a code itself. 00:15.040 --> 00:17.440 So let's go ahead and talk mode on to this part. 00:17.620 --> 00:23.320 So the next one we're going to talk about is errors now errors and how you handle them gracefully or 00:23.320 --> 00:27.130 just by default is totally up to you and how your application behaves. 00:27.130 --> 00:31.690 Now, by default, the node error handling is like really, really amazing and you don't need to do 00:31.690 --> 00:32.950 too much of the stuff. 00:32.950 --> 00:39.400 But still I like I see a lot of time that people like to handle their errors by their own and they also 00:39.400 --> 00:43.660 like to keep it different for production grade errors as well as in the development errors in the production, 00:43.660 --> 00:46.270 they send the minimum of the messages in the development. 00:46.270 --> 00:48.610 They like to keep more of the information. 00:48.610 --> 00:53.440 But I personally think that handling the error via the node itself is really fantastic. 00:53.440 --> 00:54.820 There is no such need of it yet. 00:54.820 --> 00:58.720 I'll show you that because there's just a couple of lines of code, so no big deal there. 00:58.720 --> 01:02.470 So again, it can be different for production environment as well as for development. 01:02.470 --> 01:08.950 But how you can read more about these errors, assuming that probably you haven't taken the node specialized 01:08.950 --> 01:13.150 course or not, that's up to you, but this is how we are going to study them. 01:13.150 --> 01:16.570 So go ahead and open this simple link that I've given you. 01:16.570 --> 01:18.520 This is actually a Node.js documentation. 01:18.520 --> 01:23.290 Whatever the version you are using, any advance or something not going to bother too much because these 01:23.290 --> 01:24.520 are just basic class. 01:24.520 --> 01:28.870 So you can see we have a whole lot of error class that come up like syntax errors and all of that. 01:28.870 --> 01:32.590 But I want you to bring your attention onto the very basic, which is a class error. 01:32.590 --> 01:37.720 This is the basic one which you are going to use in case you are writing a custom error class for yourself. 01:37.720 --> 01:42.100 So what you're going to notice that you can just go ahead and say, Hey, new error and you can just 01:42.100 --> 01:44.380 pass on a message to this one, and that's it. 01:44.380 --> 01:47.710 It creates automatically a kind of a message for you. 01:47.710 --> 01:54.310 It also has a property of error, code error, dot stack trace limit at a dot capture stack, trace, 01:54.580 --> 01:55.870 message and stack. 01:55.870 --> 01:58.450 And you can even customize your error code and all of that. 01:58.450 --> 01:59.620 So you can go ahead and do that. 01:59.620 --> 02:03.010 So click on here and just go ahead and try to read up here. 02:03.010 --> 02:05.680 So notice here if I want to capture this track trace. 02:05.680 --> 02:11.230 Also, it has created a simple message that, hey, this is my error and in case I want to handle this, 02:11.230 --> 02:14.500 let's just say the default is just sending me the error code itself. 02:14.890 --> 02:18.970 So what I can do is I can just write a function which takes the existing error. 02:18.970 --> 02:19.930 This is the existing error. 02:19.930 --> 02:25.330 And you can just add a method which says capture stack trace and now it will give you on what file number 02:25.330 --> 02:26.500 the errors are coming in. 02:26.500 --> 02:31.900 So this is the basic example and really I don't want to put this course into a node specific course. 02:31.900 --> 02:37.180 I want to be at a production grade back end developer, not just specific on the on the node here. 02:37.180 --> 02:41.380 But again, it is my recommendation that in case you don't understand the errors pretty well, this 02:41.380 --> 02:42.880 entire page is worth reading. 02:42.880 --> 02:45.190 And again, notice here it says new and error. 02:45.190 --> 02:47.320 And this is how you can create. 02:47.620 --> 02:52.480 You can also create a kind of a superclass on top of this one that, hey, this is my custom error handler 02:52.480 --> 02:53.920 and I just want to go like that. 02:53.920 --> 02:59.230 I want to get more information, I want to get the capture stack trace and I want to go for a trace 02:59.230 --> 02:59.560 limit. 02:59.560 --> 03:04.060 And I also want to manage my error code on my own and all of that so you can go ahead and just use that 03:04.060 --> 03:04.390 one. 03:04.390 --> 03:08.980 So creating a class on top of this is like really the basic way of how people do it, and I'll show 03:08.980 --> 03:10.030 you that as well. 03:10.120 --> 03:10.640 Okay. 03:10.990 --> 03:12.970 Now again, is it necessary? 03:12.970 --> 03:13.930 No, I don't think so. 03:13.930 --> 03:15.250 I really don't think so. 03:15.250 --> 03:20.170 I have written production, grade application, and they don't use any kind of these custom classes. 03:20.170 --> 03:24.400 The default Node.js error was able to fully handle everything on its own. 03:24.400 --> 03:25.390 So I don't need to do that. 03:25.390 --> 03:29.080 But still I'll show you that in case you are interested in that thing. 03:29.230 --> 03:34.900 Now, I would also like to give you an abstract code example of how things are there, and I would like 03:34.900 --> 03:36.580 to open up something interesting for you. 03:36.580 --> 03:40.120 So let me go ahead and open up the Mongoose documentation here as well. 03:40.120 --> 03:46.990 So let me go on to the Google and we're going to go ahead and say, Hey, Mongoose, please go ahead 03:46.990 --> 03:47.740 and open up. 03:48.520 --> 03:49.450 And there we go. 03:49.450 --> 03:51.520 So this is the thing of my browser. 03:51.520 --> 03:52.420 I type mongoose. 03:52.420 --> 03:56.380 I don't get the animal, but rather I get the mongoose ODM first. 03:56.530 --> 04:00.430 Okay, let's go ahead and read the docs and I wanted to show you something really, really interesting 04:00.430 --> 04:01.030 up here. 04:01.030 --> 04:06.640 So, okay, so I had to search a little bit to show you this, but this is really one of the most important 04:06.640 --> 04:08.890 thing that how we are going to handle errors. 04:08.890 --> 04:11.560 It actually makes sense when you come on to the mongoose itself. 04:11.560 --> 04:16.270 So as you know, that mongoose is a layer added on top of MongoDB to make server life easier. 04:16.270 --> 04:20.830 But if you just search for promises up here, so go ahead and just look for the promises that exactly 04:20.830 --> 04:21.490 what I did. 04:21.490 --> 04:24.490 I go ahead and hit search for that and it gives you all the links. 04:24.490 --> 04:28.330 The second one is most important that how Mongo is actually handle these promises. 04:28.330 --> 04:32.020 This will bring us our conversation that why we are all doing all of that. 04:32.020 --> 04:34.810 So this is the promise now it is built in promises. 04:34.810 --> 04:39.040 Yes, you can inject your promises like Bluebird and all of that, but we won't go that much off in 04:39.040 --> 04:39.460 depth. 04:39.460 --> 04:44.950 So Mongoose is a sting operation like save and queries returns the enable the word the enable simply 04:44.950 --> 04:48.700 means it returns you a promise and you can use a dot then and dot catch there. 04:48.820 --> 04:55.600 This means that you can do things like my model dot find one dot then and away dot my model dot five 04:55.630 --> 04:58.810 find one dot executed here. 04:58.810 --> 05:01.630 So what is the difference between all going up here now the. 05:01.740 --> 05:06.510 Thing is that if you're going to just run this one, this actually gives you a door then and catch back. 05:06.510 --> 05:10.260 But if you're going for the weight, it actually executes that function. 05:10.260 --> 05:15.270 And in the recent version of the Mongoose, you don't even need to write the XY because it just automatically 05:15.270 --> 05:16.130 does it for you. 05:16.140 --> 05:20.640 But the thing is, a think of it, so I know this is a little bit confusing, so let me rather give 05:20.640 --> 05:22.890 you a better example of how things actually work. 05:22.890 --> 05:27.360 So let me find up my VS code and give you a better example of how things are there. 05:27.360 --> 05:29.550 And again, I won't be giving you these files. 05:29.550 --> 05:33.000 They are not part of exercise file, they are just abstract code. 05:33.000 --> 05:37.890 I'm trying to write to just show you some stuff here so that it is easier for you to understand. 05:38.040 --> 05:42.690 Okay, so let's just say we go ahead and create a simple my user. 05:42.690 --> 05:48.060 This is going to be a simple object and it has a property of name and I go ahead and present the name. 05:48.180 --> 05:51.330 Now I want to save this name into the database. 05:51.750 --> 05:55.140 That's really as simplest of the job, what we want to do here. 05:55.320 --> 05:58.410 So how we're going to do that, let's just go ahead and create a method. 05:58.410 --> 06:00.870 So we go ahead and call this one as save user. 06:00.870 --> 06:02.130 That's how we do that. 06:02.130 --> 06:06.900 We go ahead and say, hey, request and response some kind of and again, this is abstraction code. 06:06.900 --> 06:10.140 So I'm not working on whether it is absolutely working or not. 06:10.140 --> 06:13.920 This is kind of algorithmic design or loosely algorithm. 06:13.920 --> 06:15.210 So don't pinpoint me. 06:15.210 --> 06:19.920 Please don't be like that comment section of YouTube and you are already taking a professional course, 06:19.920 --> 06:21.270 so you are very nice. 06:21.600 --> 06:23.340 Okay, so how do we do this one? 06:23.340 --> 06:27.570 Let's just say this is my model that I called up and on this model I go ahead and run the method, which 06:27.570 --> 06:30.810 is a create method which creates a new entry into the database. 06:30.930 --> 06:34.230 I go ahead and come up here and I pass on this, my user here. 06:34.380 --> 06:39.570 Now the whole idea behind that mongoose is that this entirety of the thing is actually tenable. 06:39.570 --> 06:44.430 That means you can go ahead and say dot then and you can go ahead and say Dot catch. 06:44.430 --> 06:46.410 So this is how you go ahead and do this. 06:46.560 --> 06:50.370 Now what you want to further do after this one, this all depends on you. 06:50.370 --> 06:55.470 So if the user was successfully created, it will actually return back a user to you and you can go 06:55.470 --> 06:59.070 ahead and call back like this and you can go ahead and do more stuff. 06:59.070 --> 07:03.660 So more stuff, whatever you want to do after that, maybe send a message to the user on the front end, 07:03.660 --> 07:04.650 whatever you want to do. 07:04.650 --> 07:08.040 This is one of the strategy that you might want to do. 07:08.190 --> 07:08.550 Okay. 07:08.550 --> 07:11.190 What is the another strategy that we can actually go ahead and do? 07:11.190 --> 07:13.080 Let's go ahead and try that one more time. 07:13.080 --> 07:16.680 So we're going to go ahead and say, hey, let's go ahead and define the same method. 07:16.710 --> 07:17.610 Save user. 07:17.670 --> 07:20.910 It is going to be simply request and response. 07:21.030 --> 07:24.870 Okay, further down the road, I go ahead and work on with that. 07:24.870 --> 07:27.810 So I go ahead and I want to obviously grab this user. 07:27.810 --> 07:31.170 So whatever he's saving into the user, I want to store that into available. 07:31.170 --> 07:31.890 So pretty simple. 07:31.890 --> 07:37.890 I go ahead and say this is the variable and I go ahead and say, hey user, please go ahead and create 07:37.890 --> 07:38.400 a user. 07:38.400 --> 07:44.700 For me using this, my user pretty obvious, but we saw in one of the earlier section that this operation 07:44.700 --> 07:47.010 doesn't happen like at the instant moment. 07:47.010 --> 07:51.900 So that is why in the documentation they mention this that hey, go ahead and use it await there as 07:51.900 --> 07:55.920 soon as you await there this entire method needs to be become a sync there. 07:56.820 --> 08:03.510 So this is how the basic stuff but this is not all this is not all the reason why this is not all because 08:03.510 --> 08:06.930 here you are actually handling the case where things go wrong. 08:06.930 --> 08:09.300 Here you are not handling the things which goes wrong. 08:09.300 --> 08:12.150 You are just handling the time sensitivity part of it. 08:12.150 --> 08:17.460 So how this works in this case, you are going to see that the authorized way are kind of a recommended 08:17.460 --> 08:17.730 way. 08:17.760 --> 08:21.960 Not authorized is actually to wrap all of this into a trigger block. 08:21.960 --> 08:25.980 So you need to go ahead and do some kind of try catch and just like that. 08:25.980 --> 08:31.470 So this is how things goes in and into the tribe log you go ahead and pass on this information and anything 08:31.470 --> 08:31.950 goes wrong. 08:31.950 --> 08:34.080 You actually rub that up in the try catch. 08:34.320 --> 08:39.810 But the thing is, on top of this, some time you still need to handle the promises. 08:39.810 --> 08:44.970 So even although you have written this as saying, you have written the try and catch, and if further 08:44.970 --> 08:50.640 down the road you actually go ahead and say, Hey, I still need you to handle the promises and you're 08:50.640 --> 08:53.520 going to see some console.log warning that, hey, go ahead and do that. 08:53.700 --> 08:54.930 So which one is good? 08:55.680 --> 08:57.510 Again, there is no right or wrong here. 08:57.510 --> 09:00.090 You can go ahead and go for this entirety of the flow. 09:00.090 --> 09:05.790 But the problem is sometimes you drill down so much inside of the code that some variables are not easily 09:05.790 --> 09:06.390 accessible. 09:06.390 --> 09:09.930 You need to pass on a reference of them and a whole bunch of this actually comes in. 09:09.930 --> 09:12.270 And then we have these arrow functions so we can. 09:12.420 --> 09:14.070 So there's a lot of things up here. 09:14.070 --> 09:18.540 So what you're going to see in most of the production grade code is happen something like this. 09:18.540 --> 09:21.540 So people like to go ahead and create a simple helper function. 09:21.540 --> 09:23.850 And what this helper function does is nothing. 09:23.850 --> 09:29.940 It just wraps around your entirety of the code or function that you're passing up and just puts a kind 09:29.940 --> 09:31.080 of a promise around it. 09:31.080 --> 09:32.640 So that's basically it. 09:32.640 --> 09:38.820 So let's just call this one as simply I usually call this one in all of my code as a big promise because 09:38.820 --> 09:40.110 it's kind of a big brother. 09:40.110 --> 09:45.120 So what you do is you obviously are going to receive a function on this because this entire request 09:45.120 --> 09:48.330 and response, whatever is going on, you just pass on it to as a test. 09:48.330 --> 09:50.850 So this is my function that I receive up here. 09:50.850 --> 09:56.160 Now, as soon as I received this one, I take that as a kind of an argument and I pass it on further 09:56.160 --> 09:57.270 down the road to this one. 09:57.270 --> 09:59.070 So request response and next. 09:59.070 --> 10:01.560 Next is very important in writing this help. 10:01.670 --> 10:03.650 To function further down the road. 10:03.650 --> 10:09.170 I go ahead and say, Hey, I will create my promise myself and promise. 10:09.170 --> 10:12.260 So whatever the default promise you are going to use, it's going to come in. 10:12.260 --> 10:14.140 And this promise has two property. 10:14.150 --> 10:17.870 The first one is resolve and this is how the resolve works. 10:17.870 --> 10:19.970 And the second one is dot catch. 10:20.630 --> 10:22.700 So in the catch I go ahead and say next. 10:22.700 --> 10:26.660 So that further whoever is actually running this can actually handle this one. 10:26.780 --> 10:32.450 But in the case of resolve, obviously the function that you're passing me up, I need to execute that 10:32.450 --> 10:33.440 inside this one. 10:33.440 --> 10:35.330 So I go ahead and say, hey, function. 10:35.330 --> 10:39.350 And obviously in this function you'll give me the parameters that are coming in, request, response 10:39.350 --> 10:40.640 and next. 10:40.640 --> 10:41.480 So that's it. 10:41.600 --> 10:42.830 That is it. 10:43.340 --> 10:49.190 I know this is a little bit kind of a mode for you to understand, but in case you have taken my classes 10:49.190 --> 10:53.610 on the YouTube of JavaScript of higher order functions and all of that, this is how it works. 10:53.630 --> 10:57.890 Now, once you have defined this higher order function, what is going to happen now? 10:57.890 --> 11:00.560 After that, things actually becomes a lot more easier. 11:00.560 --> 11:06.980 And you can just wrap this up around entirety of the thing into a simple big promise up here. 11:07.910 --> 11:13.850 I know this is a lot for you to digest, so go ahead, watch this video, read a little bit of the documentation. 11:13.850 --> 11:19.090 And this is kind of important thing for you to understand, either go with entirely of the dot dot catch 11:19.100 --> 11:23.780 syntax if you want to use something like holding the reference data weight and all of that, then Big 11:23.780 --> 11:28.100 Promise is definitely going to come in and we will be using that into the next section. 11:28.100 --> 11:29.370 So don't you worry too much. 11:29.390 --> 11:31.160 I'll explain that one more time. 11:31.160 --> 11:33.140 So that is easier for you to understand. 11:33.350 --> 11:38.330 I know this was this video was a little bit heavy, so go ahead, rewatch it or probably just wait for 11:38.330 --> 11:39.550 the next section to come up. 11:39.560 --> 11:41.480 Let's go ahead and catch up in the next video.