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So what's the difference between the 404 middleware?

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Basically, the resource not found middleware and the error middleware.

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And essentially, I like this explanation the best.

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Not found errors are going to be triggered If there is a request for a resource that doesn't exist.

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Something we're going to cover again one more time in one second.

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But when it comes to the error middleware, it gets triggered by the existing root.

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And this is probably confusing because the error one is the last one.

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So quite often students ask, Hey, but if I have, for example, invalid request, how come it gets

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triggered over here but it never makes it to the error one.

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And again, the reason for that is because of this middleware will take care of the requests which don't

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match anything in our server.

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But this one, the error one is going to get triggered by our existing controllers.

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Effectively, it's going to be a valid request and the error is going to pop up when we try to implement

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the functionality.

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So let me show you a good example first.

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Again, let's navigate to our Thunder client and one more time, let's make this request.

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So notice if we go to jobs with an extra S, we'll have this 404.

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So if the resource does not exist, yes, we'll trigger that 404 middleware.

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Now let's go back to the regular jobs request.

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So this should yield the list of jobs and back in the server.

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Let's make a typo over here instead of the request, let's say I want to log, but instead of jobs again,

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I'm going to go with extra s, Let's save it.

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You'll notice that actually we don't trigger the error yet, but if I go back to get all jobs and again

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send a request, I'm going to get back this 500.

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So notice.

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Again, the error middleware gets triggered by our existing root.

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So in this case, the URL, the method, all of those things were correct.

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The reason why we have 500 is because in here we had the error and essentially we'll have two types

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of errors.

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We'll have errors that are there by mistake.

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So let's say again, I just mistyped something and therefore I trigger this error or we'll have errors

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that actually we set up.

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So what am I talking about?

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Notice over here this get single job.

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So we're sending back this response of 404.

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Correct.

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But alternatively, here's what we can do.

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I can throw a new error.

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So if the ID does not match, blah, blah, blah, blah, blah.

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Instead of sending the response of 404, I will trigger the error, which in turn will trigger the error

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middleware and then we'll send back the error response.

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And if this is confusing again, we will build this a little bit later on.

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But just to give you an idea, let me go back to the get single job and instead of.

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Sending the 404.

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Notice the moment I type.

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Throw new error.

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Pretty much everything gets grayed out over here.

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Why?

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Well, because this code is not going to run.

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And let's write the same message.

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No job with that ID.

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And essentially, the moment we have this line of Code Express will handle that error right over here

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in our error middleware.

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So let me showcase that.

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Remember, every time we restart the server, we set up that array from the scratch and therefore mean

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most likely this.

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It is going to be wrong.

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And notice I click on send and I'm not getting the 404.

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Actually, I'm getting the error response because again, this middleware is going to get triggered

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in existing routes where 404 gets triggered if the resource is not available on the server.

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Hopefully that is clear.