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So we got this basic dummy server up and running but this server is not doing anything useful of course.

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Now I said I want to build a very simple REST API and for that I will actually create a new sub folder

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in the source folder which will name roots in there.

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I will add a file that should handle a certain set of roots of this REST API.

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And now it's up to you which kind of API you want to build.

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I will build to do API here.

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If you took do you react and typescript section.

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That sounds familiar to you because dear we built a to do app too.

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This is totally detached from that section though it will not work to gather with react of course you

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could connect it though on your own.

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But here I will build such a simple to do API simply so that we see how typescript works with node and

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express the application we're building is not too complex but it will contain a lot of interesting concepts.

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So here it will add my two to routes by adding a to dos dot t as file in the root folder and in there.

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I now want to use Express J S to register some roots for Dad I'll import something from Express and

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that something is now actually the router.

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Now that common J S syntax where dad typically is that you import express by using require express and

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then in a new line you off the C code where we do this here right now.

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That's something you can do.

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But here I'll just import like that now this gives us a router and we can simply call a router here

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as a function and this allows us to register middleware.

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So in the end routes and points for incoming requests where we then execute some logic upon these requests.

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Now for the to do app I want to register some basic routes opposed rout at slash nothing where we can

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add a new to do so here we'll need some code some function which then adds a to do somewhere for now

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I'll just specify no code at all.

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Just set up the route in general here so we have to post request then a get request to get all to dos

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let's say then also let's say patch request to update it to do and dare I expect to get the idea.

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Dynamic segment into you are L and then here also a delete request to delete a to do by I.D..

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These are my routes and now we can export the configured router as a default in this file.

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Now nothing will happen on these routes right.

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I haven't set up any function that would execute when a request reaches these end points but we at least

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now know which routes we want we'll add the functions in a second step later.

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For now let's just connect the router here to configured routes to our running server here in Apt.

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Yes and to do that we just import our let's say to do routes from dot slash routes to do this.

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So we're importing that export router into DOS into apt.

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Yes.

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And now here we need to connect it to our running express application by using app use and then let's

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say we want to forward all requests that start with Slash to dos to our two routes.

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So requests targeting a different you or l will not be handled there.

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Speaking of handling in the Express middleware set up here which we're using we can also set up a middleware

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that will handle errors so any errors that might be thrown anywhere in our code and we do this with

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app use and then we set up such a typical middleware function here where we get the request response

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and a next function.

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And again this all requires you to know some express J S and to know no J.S. I'll not dive into exactly

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how middleware works and express and what Middleware is right.

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So that's a regular middleware function here as you should know it from Express J.S. and you probably

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also know that there is an alternative to debt function a function that takes for Ramírez where the

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first parameter is a potential error and now it is is a error handling middleware function which will

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be fired automatically by express.

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If in any of our middleware prior to this one you have an error.

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So this my error handling middleware function and you see we got a bunch of errors here bunch of errors

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because this is all of type any.

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And we're also not using all these values.

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Let me make it clear which kind of types we have here.

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This will be of type error.

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This will be of type expressed on request or you simply import request here as an extra named import

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from expressed is also works if you've got the Express types installed which we do then here we also

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got the response and a next function here and then we can adjust our types here.

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This is now of type request.

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This is of type response and this is this next function which we can execute to let the request continue

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its journey to the next middleware in line.

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Now that's our error handling middleware.

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It will fire whenever we have an error in one of our other Middleware is in the here we could send back

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a response with let's say Jason data where we have a message which is error message and where we may

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be also set error message I mean and where we may be also set a status code of 500.

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And of course you can have a more elaborate error handling functionality than I do have it here.

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But with that we added our roots we added our error handling middleware why don't we add some logic

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to this API now in the next lecture.