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All right, and once we have the not found middleware in place, we want to do the same thing, we the

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middle way.

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And let me just briefly kind of go over the biggest differences between the two.

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And most likely, once we start setting up the controllers, we'll swing back because there's going

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to be easier for me to show you.

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But effectively the main difference is that not found one will be looking for requests that do not match

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any of our current route.

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Correct.

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Like I just said in the last video.

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But when it comes to the arrow handler, it's actually looking for errors that are happening in our

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existing world.

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And you'll see that in a second because we'll throw an error here in our home run.

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Therefore, we need to follow the rules of expression, and the rules for the error handler are following

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where essentially we'll do the same thing set up a function error handler in the middleware folder will

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create that as a function.

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But in this case, we're looking for four parameters.

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So right away, Express will know if you're looking for four parameters.

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That means that first one will be error, so it will pass in that error non-market.

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In the beginning, we'll just log it just so we can see whether everything works, and we're going to

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go with pretty generic response where we'll go with Materne 500.

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So status five hundred and nine in the JSON we'll just set up.

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There was an error.

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Now we still want to import that.

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We still want to use Jass extension, and I'm pretty much going to stop leaving this step over here.

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We'll have to repeat that to pretty much every time as we're working here in node line, I think at

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some point becomes self-explanatory and we want to place this one last one.

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And again, it's going to be easier for me to show you once we have some async errors already in our

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controllers.

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So that's why I'll put down one on ice for now.

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But please, please, please do place this one last one, even though the moment it might not look like

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a big deal.

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And if you watched my note express course, eventually our error handler pretty much is going to look

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like the one we were using throughout the course.

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The one that we were taking from project to project.

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But in this case, we'll set up everything from scratch.

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So yes, we'll start with a very basic one.

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And then each and every time we have that custom mongoose error, that's when we'll handle that.

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So this is really up to you.

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If you want to save yourself a little bit of time, you can copy and paste the code from there and you're

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good to go.

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If not, we can build it together because that's essentially what we're going to be doing.

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And yes, the last step over here showcase with a sync errors.

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So like I was saying, once we already have some logic in the controllers, it's just going to be easier

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for me to showcase the difference between the two.

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We're not found is going to be looking for all the requests that do not match any of our current route.

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And the error handler one will handle the errors that are happening in the existing route.

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And it might not sound like a big difference, but trust me, it is a big one and therefore we want

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to place the erosion all the way at the end.

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So let's actually go through the steps.

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We want to create the error handler one.

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Let's just go here with error and then hyphen and.

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Now that is going to be jealous.

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And as far as the function, I'm going to go again with the long name because my preference in the server

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is to have these names like this.

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Basically, I can do the auto import in that case as well.

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And the reason for that is because that clearly signals to me what is happening.

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Of course, this is an export default.

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So technically I can name it whatever I want.

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But in my case, I like this middleware part because that way I can clearly know what the function is

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doing.

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And then since I set that up in the file in the non-farm, I can right away use the auto import, as

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always.

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That is just my preference.

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You don't have to do that.

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So that is just a side note.

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And therefore, here I'm going to go with Konst and then error and lower and lower and lower.

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In Delaware, like I said, this function is going to be looking for for things.

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So the error first enteric virus and then the next.

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So now Express announced, OK, so this is going to be a error handler and then the first step is just

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comes along in the air and then we want to go with some kind of generic response.

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So whereas and let's set up a status that still will be 500 basically a general server error.

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We'll go here with 500 and then let's add a JSON one and then let's set up a message and we're going

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to go with what was the message over that wasn't to double check.

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So there was an error.

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So that's the one that I said might as well use that one is also there was an error.

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And then let's explore this one.

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So export.

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Default, and then we're looking for error handler.

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And now let's hop back to Sergius, look for the ninth problem and right after, not again, we're going

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to go with that use and then we'll pass in the error handler mature and we just need to make sure that

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we move this one down.

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And it looks like that in this case, it actually right away also added the jazz extension as well,

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which is really, really cool.

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So now we can test that out, and the way we'll do that is in the home run.

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Effectively, we'll throw the error.

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So say throw new error.

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And I mean, the message here is really unimportant because we already have the response in place.

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There was an error.

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So I just say here error so we can save ourselves a little bit of typing.

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So let's go back.

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Now I'm not going to be looking for for it's not shallow.

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The Iran does not exist.

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Actually, I'm going to be looking for a home Roth, and we should see there was an hour.

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And if that's what you see on a screen, beautiful, we're moving in the right direction.

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And then in the terminal, you should see the error and notice that is coming from the server address.

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And with these two middleware in place now, it can start setting up the connection to MongoDB.