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‫So in this lecture,

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‫you're gonna learn an easy way

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‫of defining parameters right in the URL,

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‫how to then read these parameters,

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‫and also, how to respond to them.

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‫Now, what we want to actually implement in this lecture

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‫is a way of getting only one tour.

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‫So right now, we have this endpoint here,

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‫which gives us all the tours,

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‫and we want to have something like this.

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‫So let's copy it into a new request for now,

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‫and then, we want slash, and then the ID of the tour.

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‫So for example, let's say five, okay?

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‫So, this is just like we talked about

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‫in the REST API lecture,

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‫where I said that if we hit this endpoint without any ID,

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‫so just like this here,

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‫well, then we would get all the tours.

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‫But if we would specify an ID after that,

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‫so, just like this,

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‫and of course it doesn't have to be an ID,

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‫it can be any unique identifier,

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‫but in this case, the easiest way of implementing it

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‫is to just use IDs, okay?

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‫So, this here is of course a variable,

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‫because it can be five, but it can also be anything else.

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‫And so this piece of the URL here,

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‫so this here, this is a variable, okay?

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‫And so what we need to do

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‫is to define a route which can accept a variable.

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‫All right, and so let's do that here,

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‫and actually right after this one.

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‫And I'm just gonna go ahead and copy it,

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‫because you already know how to write it at this point.

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‫And so, yeah.

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‫So here we have the route,

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‫and so now all we need to do is to add that variable.

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‫And that's very easy.

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‫So we have our slash again, and then the variable,

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‫we define it using a colon, like this.

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‫And so like this, we created a variable called ID.

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‫It could of course be anything else,

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‫like var, or X.

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‫Doesn't really matter.

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‫But this one is called ID, all right?

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‫Now we don't want to send back anything like this,

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‫so let's just comment it out.

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‫And what I want you to take a look at

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‫is at console dot log,

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‫req dot params.

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‫Okay, so request dot params is where all the parameters

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‫of all the variables that we define here are stored, okay?

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‫So these variables here in the URL are called parameters,

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‫and again, they are in req dot params,

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‫available for us to use now.

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‫So let's take a look now

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‫and actually do this request.

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‫And for now, it's not gonna do anything,

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‫so it will not give us tour number five

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‫automatically, of course.

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‫But what I want to do for now

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‫is to just take a look at req dot params.

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‫And so indeed, here we have, ID is five.

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‫So, request dot params is a very nice object

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‫which automatically assigns the value

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‫to our variable, so our parameter that we defined.

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‫And we could actually define multiple.

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‫So we could say ID,

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‫and then we could say X, and we could say Y,

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‫and then we, of course, would have to define all of them.

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‫So 23

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‫and 45, let's say.

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‫Send this guy.

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‫And then, indeed, we have an object

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‫with all these three variables in them.

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‫Okay, now if we define them like this in the URL,

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‫we actually have to then specify.

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‫So if we didn't have the Y parameter,

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‫we would run into an error,

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‫because we are now not hitting this exact route, okay?

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‫So our route is now no longer exactly this,

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‫but it's only this.

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‫And so, there is an error, okay?

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‫Make sense?

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‫Now there is actually one thing that we can do,

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‫and that is optional parameters.

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‫So if you want to make this parameter optional,

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‫we just add a question mark to it,

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‫and now, it is optional, so we no longer have to specify it.

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‫So just like this.

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‫And so now we only have five, 23,

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‫and then Y is still here, but it's undefined,

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‫because it's now optional.

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‫All right.

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‫But let's get rid of all of this,

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‫because we only really need the ID, okay?

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‫And so now all we need to do

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‫is to actually get the tour with this ID

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‫from our data.json, from our JSON file, right?

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‫So basically, from the tours array.

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‫And so that shouldn't be all too hard.

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‫And so let's say,

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‫const tour is equals

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‫to tours

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‫dot find.

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‫And I'm not sure if you are familiar

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‫with this find method here.

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‫So once, more this has nothing to do Node or Express,

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‫it's just a regular JavaScript function

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‫which you can use on arrays.

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‫And the way it works is this.

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‫So in here, we pass a callback function,

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‫and so let me actually start by writing that one out.

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‫So element ID

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‫equals the req

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‫dot params, okay?

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‫So it'll basically loop through the array,

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‫and in each of the iterations,

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‫we will have access to the current element,

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‫and we will return either true or false

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‫in each of the iterations, okay?

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‫Now what the find method will then do

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‫is that basically, it will create an array

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‫which only contains the element

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‫where this comparison here turns out to be true, all right?

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‫And in this situation, we want to find the element

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‫where the ID is equal to the one

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‫that we get from the parameters.

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‫And so by specifying this callback function here

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‫with this comparison, we will ensure

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‫that only the element where the ID is actually equal

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‫to the specified ID in the parameters

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‫will get returned from the find method

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‫and stored into tour, all right?

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‫Now actually, this is not going to work like this,

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‫because as you see down here,

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‫these values here, they are actually strings, okay?

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‫So we need to convert that to a number,

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‫but that's very easy.

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‫All we have to do is to say,

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‫the ID is equal to req dot params

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‫dot ID times one.

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‫So this is a nice trick where JavaScript,

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‫when we multiply a string that looks like a number,

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‫when we multiply that with another number,

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‫it will then automatically convert that string to a number.

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‫So that's a very small, nice trick that we can use here.

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‫And so, now, we already have our tour ready to send.

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‫And so the data that we want to send

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‫is tours equal

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‫to tour.

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‫Or actually, it's just tour,

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‫so tour should be equal to tour, all right?

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‫Make sense?

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‫So maybe the most complicated part here is just this one,

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‫but, yeah, that is again just a normal JavaScript.

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‫And so I believe, or at least I hope,

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‫that you're already familiar with using

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‫this kind of array methods, all right?

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‫So, we only want tour number five.

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‫And so let's take a look if it actually works.

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‫And well, it didn't, so let's take a look at that.

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‫Oh yeah, indeed, here we need to use the ID, of course.

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‫So not req.params.

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‫ID.

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‫Okay, so, try that again.

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‫And now, indeed, we have the tour with ID of five,

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‫okay, and only that single tour.

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‫Let's try number two, for example,

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‫and indeed, ID two.

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‫But now, let's try another situation.

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‫Let's do, ID 23,

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‫and so now, we get nothing back, right?

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‫And that's because there is no tour with the ID of 23,

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‫but we still return the 200 OK status code,

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‫and so, that doesn't make much sense, okay?

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‫And so let's actually go ahead and change that.

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‫And what should we do here?

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‫Well, as a very simplistic solution,

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‫what we can do is to check if the ID

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‫is larger than the length of the tours array,

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‫and if it is longer, well,

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‫then we can send back a 404 error

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‫saying that we could not find any tour for the given ID.

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‫So let's do that very simple solution,

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‫because, well, this is not the real API

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‫that we're building at this point,

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‫and in this case, it's not a problem

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‫to use an overly simplistic solution like that,

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‫because this is not the real thing that we're building here.

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‫We are really just trying to get familiar

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‫with the was that Express works.

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‫And the same thing can actually be said here, for example,

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‫when we...

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‫So down here, where we post a new tour,

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‫in the real world, we would always, always have to check

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‫if the user input is valid,

198
00:08:54,210 --> 00:08:56,680
‫so if it doesn't contain any malicious code,

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00:08:56,680 --> 00:08:59,350
‫or really, anything that we don't want in our wrap.

200
00:08:59,350 --> 00:09:01,890
‫And again, we're gonna do that, of course, later,

201
00:09:01,890 --> 00:09:03,680
‫but in this small example here,

202
00:09:03,680 --> 00:09:07,070
‫I really just want to focus on the fundamentals, okay?

203
00:09:07,070 --> 00:09:10,100
‫So let's quickly implement what we were just saying,

204
00:09:10,100 --> 00:09:15,100
‫which is that if the ID is greater than tours dot length,

205
00:09:16,570 --> 00:09:20,730
‫so for example, let's say we have 12 tours in our array,

206
00:09:20,730 --> 00:09:24,710
‫well, if the ID is then 13, or 15, or whatever,

207
00:09:24,710 --> 00:09:27,750
‫well, in that case, the ID is not valid.

208
00:09:27,750 --> 00:09:31,000
‫So, we say return, and that's because

209
00:09:31,000 --> 00:09:34,180
‫we want to exit the function right at this point, okay?

210
00:09:34,180 --> 00:09:35,823
‫And so that's why we say return.

211
00:09:37,370 --> 00:09:40,040
‫Then we send a status of 404,

212
00:09:40,040 --> 00:09:42,893
‫because we couldn't find any tour for that ID,

213
00:09:44,106 --> 00:09:46,370
‫and then a simple JSON response

214
00:09:49,400 --> 00:09:51,563
‫with a status of fail.

215
00:09:52,740 --> 00:09:56,173
‫So fail is what we send whenever we have a 400 code.

216
00:09:58,180 --> 00:10:00,053
‫And then just a message property,

217
00:10:03,580 --> 00:10:04,663
‫invalid ID.

218
00:10:06,640 --> 00:10:07,820
‫All right.

219
00:10:07,820 --> 00:10:09,503
‫And so let's test that now.

220
00:10:10,740 --> 00:10:12,103
‫So we have our 23.

221
00:10:13,340 --> 00:10:16,900
‫And, indeed, 404 not found, invalid ID.

222
00:10:16,900 --> 00:10:19,810
‫So that's exactly what we just did, and,

223
00:10:19,810 --> 00:10:22,093
‫it looks like it's working, okay?

224
00:10:24,230 --> 00:10:25,860
‫Another solution that we could

225
00:10:25,860 --> 00:10:27,490
‫of course implement here as well

226
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‫would be to just do this test

227
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‫after we do the tour here.

228
00:10:34,440 --> 00:10:36,100
‫So we would get the ID,

229
00:10:36,100 --> 00:10:38,230
‫then we would try to find a tour,

230
00:10:38,230 --> 00:10:39,810
‫and if there was no tour,

231
00:10:39,810 --> 00:10:42,670
‫well then we would say that the ID is invalid.

232
00:10:42,670 --> 00:10:45,600
‫So let's comment out this one, duplicate,

233
00:10:45,600 --> 00:10:48,950
‫just so that we actually keep both solutions here.

234
00:10:48,950 --> 00:10:52,000
‫And so we can say, if there is no tour, okay?

235
00:10:52,000 --> 00:10:53,970
‫So basically, the result here,

236
00:10:53,970 --> 00:10:56,190
‫if there is no tour found,

237
00:10:56,190 --> 00:10:59,130
‫well then this variable is basically undefined,

238
00:10:59,130 --> 00:11:01,840
‫and we can then test for that here, like this.

239
00:11:01,840 --> 00:11:05,790
‫So if there is no tour, so if tour is basically undefined,

240
00:11:05,790 --> 00:11:09,183
‫well, then we send back this error message.

241
00:11:10,330 --> 00:11:12,010
‫So let's test that as well.

242
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‫And so indeed, it gives us the same result.

243
00:11:14,820 --> 00:11:16,590
‫Okay, and just like that,

244
00:11:16,590 --> 00:11:18,750
‫you learned how to specify parameters

245
00:11:18,750 --> 00:11:21,680
‫in a URL, like this, okay?

246
00:11:21,680 --> 00:11:24,470
‫Then you learned how to read these parameters

247
00:11:24,470 --> 00:11:27,650
‫from the URL, by using req dot params.

248
00:11:27,650 --> 00:11:31,650
‫Well, and then we used that ID, so that parameter,

249
00:11:31,650 --> 00:11:35,140
‫in order to find a tour with that exact ID.

250
00:11:35,140 --> 00:11:38,210
‫So that's what we did here, in this line, okay?

251
00:11:38,210 --> 00:11:40,520
‫So that was the goal for this video,

252
00:11:40,520 --> 00:11:42,843
‫and so let's now move on to the next one.