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In this video.

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Let's go ahead and refactor our error handling inside our root.

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You can see that any time you want to throw an error unless you go through this process.

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So let's find a way where we can centralize this one.

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So let's go ahead and create a folder for this.

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So I'm going to create a folder called Utils.

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And inside I'm going to create a file called App Error.

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I make use of uppercase because we are going to create this one using a class.

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So in case you are not familiar with classes in JavaScript, don't worry, I will create a different

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function where we are going to use normal function syntax.

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So first let's use normal function syntax here and then after that I'm going to show you how we can

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make use of classes in JavaScript to achieve the same concept.

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So here we go.

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Before we start the implementation, let's look at the arguments or the properties the function needs.

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First of all, it needs the status code, the message, and this are the most important thing here.

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For starters, we always know it is failed so we can choose not to provide and we can give it as a default

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value for that.

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So let's send this to arguments starters and then the message.

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All right, So here we go.

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So make use of costs and then the app error is equal to error function.

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And for this function, I'm going to take in the message of the error and then the status code that

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we want to provide.

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So inside here we are going to create instance of the error from the error class, which is equal to

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new and then the error.

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And for this we are going to pass in the message because for this error, the only argument it takes

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is a message we pass into this class.

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So now here next is let's add the status code.

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So the error dot status code, which is equal to the status code that we pass in.

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Lastly, we need to return the value for this function.

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So going to be the error and let's export this module.

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Dart's export is equal to our error.

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Now inside the server file, any way I want to throw an error, I'm going to call that function.

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So let's require the error function here and now we are going to remove all this code from here and

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are going to call the app error.

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Then you pass in our message, which is network.

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Error.

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And then the second argument is going to be the status code, which is 500.

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So what comes back from this one is the actual error.

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So cost the error here and next is going to pass in to the next maneuver, which is down here.

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So now let's make the request and let's see.

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We can see that we have network error.

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And then with the status code 500, that is internal server error and we can call the same function

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here in any root.

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For example, this log in here.

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So now I'm going to call the function here and here the message is going to be as you are not logged

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in and 401 meaning not authorized.

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Now let's go to the file and let's hit send.

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And there we go.

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We got a message.

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But the problem is we are not getting the status code is always 500.

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So let's see what is wrong.

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Oh, sorry.

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We need to send the error for this function call.

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So now let's remove this one.

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And next is let's pass in the error here.

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So let's make the request.

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And we got the status code for one with a message.

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You are not logged in so well from this one.

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Let me make sure I type in the correct.

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Yeah.

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Okay.

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So again, let me show you one more time.

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And indeed, we have it.

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So this is one way where we can create a function to create an error.

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But if we want to use class based one, let me show you this one or so.

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So let me comment this one.

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So here we go.

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Make use of class and then uppercase up error because we are going to create an instance of this error

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and we need to extend from the error class as that.

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And next is I don't.

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And next is our brain and mind function called constructor.

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And it's going to be called when an object is created from this class and I'll pass in the message of

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the error and then the status code also.

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Next is we will call the super.

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Then you pass in the message because for this it takes in only one agreement.

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That is a message.

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So let's go ahead and add the status code to it, which is equal to the status code.

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So let's go ahead and export this one.

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We can remove this one and make use of app error here.

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So next is inside any route I want to call, I'm going to make use of that.

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So let me change this one to uppercase app error.

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So next is let's modify this function or let's change this one to uppercase A, And because it's a class,

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we're going to make use of new to create an instance of this class.

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So now that is it.

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So let's go ahead and make the requests and now let's check it out.

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You can see that network error and is working fine.

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The same thing applies to the profile.

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Make use of this uppercase up error and then name equal to that.

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And let's send the requests and we have the network error and also we call something stock trace stock

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trace is a code on a file where that particular error occurs.

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So for this one, we can see that it is giving us the message.

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But if you want to know what file does this error okay, you're going to use what is called the stock

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trace.

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So inside the error handler here where we are catching the error, we can also throw the stock trace

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also.

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So here are going to be the stock.

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And we have access to the error dot stock.

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Now save it and let's make the request.

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And now we can see that this time around I get beautiful message with the stock, meaning the file that

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this error occurred and what line.

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So if you look through, have a look can say that this is the file and then if you look through it,

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you're going to see the particular line that this particular error.

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Okay.

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So it's somewhere unless you take your time and then look through.

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Well, you can see that it starts from here and then it ends somewhere here.

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That is my server dot just filed on line number ten.

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So if I check my server file, line number ten, let's see.

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And this is where the error.

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Okay, so start trace, help us to debug our code where a particular error.

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Okay.

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So the next step is how can we handle asynchronous errors, for example, when we are dealing with database?

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So let me show you how we are going to do this one in the next video.