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So we have these messages here, which are loaded

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from that dummy backend, which is a separate process,

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a separate server running in the background.

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Now, if you open the terminal

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and you go to that window where you start

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at the backend server

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and you reload this messages page

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where we see those messages,

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you should see some log messages here.

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If you don't, delete this .next folder

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in your NextJS project,

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then quit that backend server

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and restart it.

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And most importantly, quit the NextJS

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development server and also restart that.

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And then thereafter, in the terminal

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where you start at the backend server,

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if you then reload, you should definitely

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see those log messages.

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And you should see two log messages here,

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because in my NextJS application,

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I actually got two requests to that backend.

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In the messages folder, I have that layout JS file.

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And in there, I have one request to the backend

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where I fetched the messages.

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And in the page JS file, I got one request.

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So two requests sent to the backend.

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And as you see, these two requests lead

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to two request logs.

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Now, if you paid close attention,

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this might sound a bit weird

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because I did mention this request memorization,

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which was a mechanism built into NextJS

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to avoid duplicate requests to the same data source.

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And indeed, here I have one and the same data source,

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one and the same backend server,

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and I'm sending a request to that server

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from two different places.

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And that seems to lead to two different requests,

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as we can tell by these backend logs.

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And that's exactly what should be avoided.

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And indeed NextJS has a mechanism

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that avoids duplicate requests as we see it here.

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But that mechanism is only active

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if those requests are sent with exactly

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the same configuration.

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And here, I'm talking about requests sent

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with the fetch function.

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Later, I will also show you how to avoid

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duplicate requests to other data sources

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like your own database

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to which you reach out directly from

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inside the NextJS application.

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We can also avoid duplicate requests to that,

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as you will see later.

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But for now, it's about duplicate requests

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to a separate backend, which we clearly have here.

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And we have those duplicate requests

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because the request I sent here

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in the messages page component

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and the request I send in the messages layout

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are not exactly the same.

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They have a different headers configuration,

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and I set up this different configuration

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so that on the backend,

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I can log which exact

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place in the front end did send the request.

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I'm extracting that headers data here,

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and I'm logging it here, but therefore,

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I have different requests with different configurations.

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Now, what you will see is that if I get rid

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of this headers configuration in my NextJS application

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here in the messages page,

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and then also, in the messages layout,

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and I then save the code,

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I have exactly the same

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request signature in both places.

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And if I do that and I then go to my backend code,

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again, you can already see that only one

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new request was added to it here.

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Now, if I reload this messages page,

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you will see that actually no new request is sent here.

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And I'll get back to why that's the case later.

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You can always delete this .next folder though

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to reset the NextJS application essentially,

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because that .next folder holds some temporary data,

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some cache data that's used by the next application.

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And if you delete that folder

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and then restart the next development server,

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it will be recreated with fresh data.

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And if you do that

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and you go to that backend page again,

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you will see that now,

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if I maybe also restart that to clear the logs here,

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that now, if I reload that messages page,

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only one new request is added here.

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And keep in mind that earlier we had two requests,

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one from the layout, one from the page.

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Now, since I'm not sending those extra headers,

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which were different anymore, I can't tell

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where this request is coming from, but I can tell

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that it's only one request instead of two.

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So that's that request memorization in action here.

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And that's one key mechanism built into NextJS,

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which you get for free.

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Whenever you have two requests

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with exactly the same configuration.

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In this case here, fetch requests sent to a backend,

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NextJS avoids unnecessary requests,

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and instead just sends one request

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and then reuses the response in all the places

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of the application that needs the response.