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Let's get started with express Middle words.

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We have two types of middle words.

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One is custom materials.

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That is materials that we are going to create by ourselves.

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And we also have third party middleware where we can download from NPM registry.

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So in this video, we are going to work with custom media words.

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So back to Visual Studio Code.

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I have already created a simple express server with few lines of code.

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And I'll provide this file for you.

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But if you want to use your custom express server, you can go ahead and do so.

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So let's go through this code line by line.

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We have the first route, which is home route, which sends hello word to the user.

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The next route is a logging route.

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And this one send logging successful.

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And the next route is a route to create post.

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And all what is doing is just to send post created.

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And for the description we have row which is authenticated user.

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Meaning that this route you need to be logged in before you can use this route.

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Well, we have not talked about authentication and authorization yet, but let's try to mimic.

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All right.

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So it means that this route you need to log in before you can create a post.

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And the next route is to fetch all posts.

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And for description, it says that public meaning that whether you have logged in or not, you can still

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have access to this route.

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And the last route is to delete a post.

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So for this action, unless you are an admin before you can delete a post.

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So how can we achieve all this logic?

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Well, we can do so using what is called middleware.

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So how can we make use of middleware?

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The first step is we need to create it.

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So let's have a route map.

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The first step is what creates middleware.

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I start.

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So let's go over again.

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What is middleware?

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So middleware is a function that have access to the request and the response object.

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And if you have access to the request and response object, it means that we can do whatever we want

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with it before we send the response or before getting to the server.

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So here we go.

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Since middleware is a function, we can use normal function syntax to create middleware.

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So the middleware that we are going to create is called logger, which means that any time a user visit

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any of our root, we want to display a message to the console.

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So let's see how we can create that.

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For this one, I'm going to use a function.

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You can use normal functions syntax.

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So let's go.

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The first step is the name of the middleware, and I'll call it as logger and equal to my error function.

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And this is a normal function syntax.

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The next step is the argument that this function takes For many words.

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It takes in three arguments.

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The first one is a request.

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Second one is response, and the next one is called next.

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So these three arguments, the first one represents the request the user is making, and then the response

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is what is going to be sent back to the user?

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And the next is a function.

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Do you remember we've talked about the next function in the previous video.

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So the next function is a function that allows another murderer to proceed in the pipeline or in the

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chain.

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And I'll show you in just a second.

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So inside the function body here, we can make use of any logic here.

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For the meantime, we are just console.log in a message.

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Says that a logger middle.

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Where.

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So now we have created our first middleware.

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How can we use it?

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So let's have a comment.

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Says Use middleware.

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So how can we use it and express make it pretty simple to plug in modules.

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And here you go.

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We make use of app on that.

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We have what is used and the app is an instance of express and we have a method called use.

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So you simply means that we are plugging in or we are using another function, which is what middleware

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to enhance the functionality of our server.

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So with upload use, we can plug in any function where we can add our own logic into it.

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And the first one is called the Major world.

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So we pass in the logger middleware and don't call it as this, but instead what use is going to call

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the logger for us, and that is our murderer.

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So now when I save it, make sure that your server is up and running.

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And let's get back to Postman and I have created a collection called Middleware.

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And inside I have one request to fetch our post.

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So I'm trying to hit this route called Fetch or Post.

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So let's scroll down here and this is a route I want to hit.

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So now have a look when I hit send.

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Now you can see something going on here.

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Two things are going on here.

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First one is we are not getting the response from the root and we see what is called sending requests.

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The next step is if you check our terminal, we have a message that I'm a logger, which means that

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our middleware has been called, but we are not getting the response from the root.

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So why is it so?

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Well, the first point is that any time you make a request to any of our root, this middleware function

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will be called.

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The next step is that unless we manually tell, express that please proceed to the next network.

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That is why the next function is very important here, or it shines here.

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So here to be able to allow Express to proceed on to the next middleware we are going to call next.

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And this function is given to us by express automatically and we can name it whatever you want.

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It can be anything.

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But by convention we make use of next.

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So when I save it now, when I cancel the request, now you see that our server has hang out.

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Now let's make the request again.

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And you can say that now I get my response and I also get my middleware message.

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So now you can see how important the next function is.

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So the next function allows experts to move on to the next middleware.

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So we be asking, we have only one middleware.

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So what is the next middleware?

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Remember, the root handle is and this is our root handler.

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Let me show you after our path here, we have the callback function and this is our request handler

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and is a middleware also.

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So the first step is that as soon as we hit that root, first is going to call the middleware, this

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middleware here.

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And then if it is next here, then Express will push on to the next middleware, which is this root

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that you called, which is this root that we call this one.

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So this also a middleware.

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All right.

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So now this is how you create a murderer.

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So in the next video, let's go ahead and create a mature where it can display a message that please

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log in before you can access it.

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Let's get into that in the next video.