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So like I mentioned in the previous video, I've been getting some questions why this order is important,

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so essentially why replace or for beforo around one?

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And let me show you with an example.

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So at the moment, I only have the homepage route correct.

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So we have to get something for for Slashdot, our home page.

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So pretty much if I'm going to look for for its lush apples, I should get the four or four correct

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because Root does not exist.

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So let me navigate back to your browser window and I'm going to be looking for localhost 5000.

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And let's just type here Apple's.

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And once I hit the root, we should see Root does not exist.

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Correct.

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Now let's think about why is it happening?

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Well, once the user gets their old brand, express is like, OK, let me check all the root.

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So first we run through all the Midwest, which in this case, it doesn't really matter because we don't

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have the JSON data to begin with.

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But regardless, we still go through this middleware first, then Express tries to hit all the roots.

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Now, in this case, we only have one, but the same thing would work.

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Let's go back to.

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I don't know which one.

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When I wore out, I think it was the jobs one.

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Sorry for the detour, but this is very, very important.

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Well, we have the Midwest, correct?

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And then we have roots.

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In this case, it's set up with a router, so this will still work the same way regardless.

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In this case, we just have one root, and that's why it's pretty easy to show you.

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So Express tries to hit all the roots in this case only homepage, and if it doesn't find the root,

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you automatically end up over here.

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That's very important.

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That's the 404.

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That's why if I go to forward slash apples, I'll get the 404.

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And also notice something interesting where in the forum for.

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We are not calling next.

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Once we hit the four or four, that's it.

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We are done.

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We're saying, Hey, rule does not exist in this project.

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Hopefully, that is clear.

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So therefore, we place this for 04 after all the droughts.

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And now the next question is, well, why don't we place the air handler one before the four or four?

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Well, because by express rules, we need to set this one as the last one.

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And when it comes to invoking this one, well, this middleware, actually, we invoke it from the successful

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request.

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Now what am I mean by that?

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Well, if I go back here to the home page?

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And in the controller, if I'm just going to go throw new error and I'll just say there, hello there,

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and if I'll say it and if we'll go back to localhost 5000 basically a whole world, you'll see this

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message.

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Hello there.

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Why?

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Well, because of this one error handler one is invoked in the actual existing route.

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So there's no way for you to get this error handler one unless you actually hit the existing route.

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If there is no route, she's going to check all that out and is going to say, All right, so here it

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is.

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Here it is.

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Four or four.

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Now, this one on purpose per express rules, is set as a last one.

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Because of this one, we only hit from the existing around.

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So you won't hear it from the random route and just get the error.

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That's not how it works.

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Only if in one of the existing routes, you throw an arrow like we do with our custom ones, only then

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is going to be handled over here.

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Hopefully, I made myself clear and hopefully answered all the questions.