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Now in the previous lectures,

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I talked about handling errors that can occur.

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And I talked about the 404 error,

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which means that a resource is not found.

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An error, typically cost by the client

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requesting an invalid resource

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and I talked about the 500 error,

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which is a service site error.

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Now these numbers are really just the status codes that we

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typically use for communicating these kind of errors.

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And I did talk about status codes before already.

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I did say that that we typically have this 200 status code

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as part of the response to signal that the request succeeded

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and we are able to send back a valid response

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and that'd be, for example, have 404 or 500 for the errors

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I mentioned in the last lectures.

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There also are other status codes, like 401, which is,

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for example,

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typically sent back if a user is not logged in and tries to

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access a resource that requires logging in.

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For example,

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if you try to purchase a product on Amazon and you want to

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go to the checkout page without being locked in,

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that could be scenarios for that.

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We'll see that status code 401 later.

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There also are many other status codes.

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Attached you find a link to all the available status codes

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and we'll see some of them throughout this course,

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the most common ones.

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But there is one problem with those status codes.

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It's nice that we have them

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and it's nice that I named my files 404 EJS and 500 EJS.

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With that, at least to us as a developer,

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it's clear which template is used in which scenarios.

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But if we have a look at the running application,

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we actually don't see the status codes there.

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If I enter an invalid, URL here.

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If I try to access a restaurant that doesn't exist,

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I get this 404 page

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and that is all a typical user should see.

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But technically we are not returning a totally clear or

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correct response

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and you can see that this is the case

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if you open your developer tools and go to the network

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tab there.

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If I reload this page,

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we see all the requests that were made

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and if we click on the top most one,

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which is the request to the HTML page itself,

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I indeed get this kind of status code,

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a 304, not modified.

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Now here, we actually see a 304 status code instead of 200.

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The only reason for that is that Chrome,

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the browser I'm using here is actually caching old responses

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for me,

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which means it's basically saved these downloaded HTML files

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or the HTML content locally on my computer to serve them

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quicker for a subsequent requests,

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and that's why I'm seeing a different status code here.

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I could disable this by checking this disabled cash check

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mark here in the network tab

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and then I would see the 200 response.

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Since I haven't disabled this here,

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If I reload this, I get the 304 response.

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But 300 dish status codes,

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so status codes in the 300 hundred area,

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as well as 200 dish status codes

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mean that the request was successful

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and you did get the response that you requested in the end.

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And that's the wrong message here,

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because this is not the response we requested.

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We want the details for the restaurant, with this ID.

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And what we got is a page that tells us that this restaurant

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doesn't exist. That's not a success, that's a failure.

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And therefore we should also communicate that with the

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status code, by setting a errors status code here,

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even though that won't affect, what's visible on the page.

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That's important, that won't change.

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The page content will always be what you see here,

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but still we want to communicate the correct status code,

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the technically correct status code

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to the browser so that the browser, for example,

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does not save cache this error page locally,

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but that the browser knows that for this request,

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so for a get request to this URL,

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we did not get a success response.

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We want to make that clear and at the moment we aren't.

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And to be technically correct,

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you can dare for all the call and never method on this

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response object here before you call render.

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And that's the status method.

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Now what I'm doing here is called chaining.

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I'm calling a method after calling another method.

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So I'm calling this render method on the result of calling

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status and status simply returns us

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an updated response object.

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So I'm technically still calling render on my

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response object, but on a slightly updated one.

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And what did change well,

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status allows me to set a custom status code

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and the default would be 200.

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Here, I do want to set it to 404

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and hence me simply pass 404 as a

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number to status.

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And here, when we render 500, I will set this to status 500.

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And in the other place where we have a 404 error,

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Here,

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when we don't find a restaurant with that ID,

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I also call status first and set this to 404.

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Now, if we save all of that

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and we opened the developer tools again,

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if I reload this page now,

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you'll see the request is a red,

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and now we have data appropriate status code here.

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Now to the user who doesn't use these developer tools,

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nothing changes on the screen.

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Still, this is technically more correct

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and it can have an impact, for example,

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on some optimizations, the browser might perform.

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That's why we should be correct technically

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even if the user doesn't directly see

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that changed status code.

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Now over the next lectures,

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you won't see that code anymore because I added this after

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recording the next lectures,

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because originally I planned on showing this later,

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but plans changed

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and this is important to understand right now,

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because this now is a technically valid 404 response with

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our 404 page content and the appropriate status code to

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clearly communicate to the client,

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to the browser, that this is a response,

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but not the expected one.