1 00:00:00,200 --> 00:00:03,710 So what I want to do now is create a custom error handler. 2 00:00:03,710 --> 00:00:09,110 So whenever we have any errors, whether there's, you know, there's product we're trying to find that 3 00:00:09,110 --> 00:00:16,820 doesn't match the ID or whatever, it always it always shows the same thing, an object with a message 4 00:00:16,820 --> 00:00:19,250 and also the stack trace. 5 00:00:19,250 --> 00:00:24,740 If we're in development and you can you can have your errors formatted absolutely however you want. 6 00:00:24,740 --> 00:00:26,650 But I want to just keep it simple. 7 00:00:26,660 --> 00:00:32,840 Now in Express, there's a default error handler and if you want to overwrite it, you can do that. 8 00:00:33,110 --> 00:00:42,530 Let's see by just creating this a function called error handler and pass in error as the first argument 9 00:00:42,530 --> 00:00:43,070 here. 10 00:00:43,070 --> 00:00:48,770 And then you can do whatever you want as far as statuses and messages and all that. 11 00:00:49,010 --> 00:00:54,440 Now, what we did with the async handler is actually an example right here. 12 00:00:54,650 --> 00:00:56,300 So see this right here? 13 00:00:56,300 --> 00:01:00,390 This this promise resolve dot then. 14 00:01:00,390 --> 00:01:04,920 And basically this is what we did with the async handler. 15 00:01:04,920 --> 00:01:12,150 So this will avoid the overhead of try catch blocks when using functions that return promises. 16 00:01:12,150 --> 00:01:14,910 So that's why we added that async handler. 17 00:01:14,910 --> 00:01:19,470 But what we're going to do is create let's just close this up for now. 18 00:01:19,650 --> 00:01:22,980 Let's create in our back end middleware folder. 19 00:01:22,980 --> 00:01:25,410 Let's create a file called Error. 20 00:01:26,340 --> 00:01:28,010 Middleware dot. 21 00:01:28,050 --> 00:01:33,010 JS And there's basically two functions that I want to create here. 22 00:01:33,030 --> 00:01:39,600 The first one is going to be called NotFound, and basically this will this will be called if no other 23 00:01:39,600 --> 00:01:46,110 middleware has handled the request and it will create a new error object and set the code to 404, which 24 00:01:46,110 --> 00:01:47,820 is a not found error. 25 00:01:48,090 --> 00:01:48,420 All right. 26 00:01:48,420 --> 00:01:53,730 So basically, we're going to create a variable, set it to new error, and we're going to pass in a 27 00:01:53,730 --> 00:02:00,000 message of not found dash and then the original URL, which we can get from the request object. 28 00:02:00,000 --> 00:02:06,700 And then we set the status to 404 and we call the next piece of middleware passing in that error variable. 29 00:02:06,720 --> 00:02:14,520 Now to overwrite the default express handler error handler, we're going to create a function called 30 00:02:14,520 --> 00:02:15,690 error handler. 31 00:02:16,440 --> 00:02:16,760 All right. 32 00:02:16,800 --> 00:02:23,430 And then and that gets passed in not only requests response next, but also error at the beginning. 33 00:02:23,670 --> 00:02:27,810 So I'm going to initialize a couple variables here. 34 00:02:27,810 --> 00:02:33,290 So let's say status or status code, and I'm going to set that to a ternary. 35 00:02:33,300 --> 00:02:40,080 So we're going to check to see if the status code is 200, because it may be if we're throwing an error, 36 00:02:40,080 --> 00:02:48,990 we want to be able to throw an error from anywhere by doing this, say throw new error and then pass 37 00:02:48,990 --> 00:02:50,130 in some message. 38 00:02:50,130 --> 00:02:51,480 So we want to be able to do that. 39 00:02:51,480 --> 00:02:55,440 And if it's 200, I want it to change to 500. 40 00:02:55,650 --> 00:02:55,980 Okay. 41 00:02:55,980 --> 00:03:01,310 If it's anything else like 404 or whatever, then that's what it's going to stay. 42 00:03:01,320 --> 00:03:01,620 Okay. 43 00:03:01,620 --> 00:03:03,990 So it'll be whatever that status code is. 44 00:03:03,990 --> 00:03:06,370 So if it's 200, it'll be 500. 45 00:03:06,390 --> 00:03:09,900 If it's something different, it'll stay whatever it is. 46 00:03:10,080 --> 00:03:15,930 Then for the message, let's say let message equals and then error message. 47 00:03:15,930 --> 00:03:20,760 So if I say throw new error and I pass in a message, we can access it from here. 48 00:03:20,760 --> 00:03:23,220 And that's what we're setting to this variable. 49 00:03:23,400 --> 00:03:33,220 Now I want to check for let's say, yeah, we can say that mongoose bad object ID or cast error. 50 00:03:33,220 --> 00:03:36,430 And I showed you an example of that in the last video. 51 00:03:36,430 --> 00:03:44,560 If we get a single product and we pass in an ID that doesn't exist, it gives us this HTML page with 52 00:03:44,560 --> 00:03:47,110 a 500 status. 53 00:03:47,110 --> 00:03:54,430 And if this is a cast error, so I want to check for this and show something different if that does 54 00:03:54,430 --> 00:03:55,270 happen. 55 00:03:55,270 --> 00:03:59,110 So we need to first of all, we're going to say if. 56 00:03:59,880 --> 00:04:00,690 Yeah, we can do that. 57 00:04:00,690 --> 00:04:01,710 So if. 58 00:04:02,650 --> 00:04:03,370 Error. 59 00:04:05,430 --> 00:04:06,270 I'll just type it out. 60 00:04:06,270 --> 00:04:10,440 So if the error name is equal to cast. 61 00:04:11,530 --> 00:04:17,709 Error, but I also want to check the kind so there's this kind value on the error. 62 00:04:17,740 --> 00:04:18,519 Object. 63 00:04:18,519 --> 00:04:21,370 And we want to check to see if its object ID. 64 00:04:21,820 --> 00:04:29,110 If so, then we're going to set the message that we initialized up here to resource not found and we're 65 00:04:29,110 --> 00:04:31,930 going to set that status code to 404. 66 00:04:32,260 --> 00:04:32,650 Okay. 67 00:04:32,650 --> 00:04:38,290 Then we want to just do our final response, which is going to be, let's say res dot status. 68 00:04:39,120 --> 00:04:42,980 And we're going to pass in whatever that status code is. 69 00:04:42,990 --> 00:04:51,450 And then the Json, which is just going to be basically an object with the message. 70 00:04:52,210 --> 00:04:55,210 From the message variable, so we can just keep it like that. 71 00:04:55,210 --> 00:05:02,980 And then I'm also going to send the stack trace, which can be helpful for developers if we're in development. 72 00:05:02,980 --> 00:05:09,880 So if it's in production, it's just going to send this this pancakes and a stack of pancakes else. 73 00:05:09,880 --> 00:05:14,170 Then it's going to send the actual stack to stack trace. 74 00:05:14,770 --> 00:05:17,320 All right, then we just want to export these. 75 00:05:17,320 --> 00:05:21,160 So we'll say export not found an error handler. 76 00:05:21,160 --> 00:05:27,850 And then to use these, we have to go into our server.js and first of all, bring them in. 77 00:05:27,850 --> 00:05:35,590 Let's say import not found an error handler from middleware slash error middleware. 78 00:05:35,620 --> 00:05:44,200 JS And then we're going to go down here under all the routes and say app dot use not found and app dot 79 00:05:44,200 --> 00:05:45,700 use error handler. 80 00:05:45,700 --> 00:05:52,880 So now what I'm going to do is in our product route where we test to see if there's a product, we respond 81 00:05:52,880 --> 00:05:59,510 with it else instead of doing this, which isn't even working because that cast error is is taking control. 82 00:05:59,510 --> 00:06:05,540 Instead of doing that, I'm going to use our new error handler by first setting the status to 404 and 83 00:06:05,540 --> 00:06:11,060 then throwing a new error and just saying product not found or, let's say resource. 84 00:06:12,310 --> 00:06:13,930 Resource not found. 85 00:06:13,930 --> 00:06:19,540 So now let's come back over here and let's get the product with one with the ID of one which doesn't 86 00:06:19,540 --> 00:06:20,530 exist. 87 00:06:20,530 --> 00:06:23,620 And now you can see we get a 404 response. 88 00:06:23,650 --> 00:06:27,760 We get a message resource not found, and then we get the stack trace. 89 00:06:27,760 --> 00:06:32,380 So no more HTML page, which doesn't make sense for a Json API. 90 00:06:33,720 --> 00:06:34,050 Okay. 91 00:06:34,050 --> 00:06:40,350 And if we want to throw any error, like let's go to our products route and just say throw. 92 00:06:41,350 --> 00:06:45,280 New error and just say some error. 93 00:06:45,280 --> 00:06:52,420 So now if I go to my products, get all products and I send we get a 500 because we didn't set it to 94 00:06:52,420 --> 00:06:53,170 anything else. 95 00:06:53,170 --> 00:07:00,400 Remember, if it's if it's 200, it just gets sets to 500 some error and then we get our stack trace. 96 00:07:01,280 --> 00:07:07,550 Okay, so that little bit of code that we added makes things much more elegant when it comes to handling 97 00:07:07,550 --> 00:07:08,000 errors. 98 00:07:08,000 --> 00:07:09,770 We just do throw new error. 99 00:07:09,800 --> 00:07:13,610 We can set a status right before it and we're all good. 100 00:07:15,210 --> 00:07:15,570 All right. 101 00:07:15,570 --> 00:07:21,750 So the last thing I want to do on the back end before we move back to the front end is create controllers. 102 00:07:21,750 --> 00:07:27,990 Instead of putting all of our logic in the root file, we're going to have a controllers for products, 103 00:07:27,990 --> 00:07:31,830 users and orders and put all of our functionality there.