Welcome to the tutorial, Error Handling. Preserve all university, this is Scott Butler. In this demo, we're going to go through some examples of error handling in your solution. At various times, you're going to have to deal with handling different errors that may pop up throughout your application. So I've got a little example here that I built and I have a form based on some customer table and I have a test button. Let's open up this test button and see what it does. So what I'm doing here is I've got a function called join and it's basically taking and parsing a name. So we've got one field that contains the full name and we're taking and parsing that and we're flipping it so that we can display last name, commas and then a space and the first name. And my test event is simply just calling that function and then displaying it. So let's run a simple test here. So I've got Maria Anders and if I click test, I can see it alternates that name for me. I can scroll down to a couple of other ones and I can see again that function is working fine. Normally the type of one of the key types of errors that you'll deal with is data that you didn't really expect. So I'll make a new record here and I'll type in a company ID and let's type in a company name. I'm going to click my test button. Notice my contact name that I'm parsing is empty and what do you know now I've got an error message. And so if I dig through my error console here, I can see it's not able to call the method substring of null. So what's happening here is when the name is null, I'm airing out because of course it's empty. One of the defensive coding techniques that you should be doing is in reality you should first be checking the input parameters. So you would first check to see whether or not the name is null or not before you continue. But in this example we're just going to deal with the error handling side of things. So what we can do in JavaScript is what's called a try catch routine. And we've showed this a little bit earlier in the JavaScript tutorial but we'll cover it again. So we've typed in try and we put the code that we want to run normally and then we've put this catch and notice that inside of catch we've typed in E. That's because whatever error happens gets passed into E. And then we're going to go ahead and log that error out and the message will be E. And then with the log level, if we come down here to application and constants there's a logging level and I can log it as an error. And I want to return something here so I'm just going to return back empty text. Actually what would be better is just to turn back null. So let's go ahead and run this again. And so now you can see it just outputs null. So what's happening here is if we actually want to step through this I'll turn on debugger and as we walk into this the error happens on the first line and so it automatically jumps into the catch statement and does I return. The other option that we have is a finally block. So if you're doing something like initializing some global variables or something like that and you're going to reset those after they're done finally is a great place to do that. So what's going to happen is try will run and if it runs normally everything will execute fine it'll skip over catch and it'll run the finally code. If there's an error that happens while we're in the try block we'll go into the catch block and then we'll go into the finally except for here of course we wouldn't because of the returns. So an alternate way to code this would be something like that we'll declare a variable up top and we're going to set our variable throughout the program here. And so now what we have is we're going to return something inside of the finally block. And if we run this we can see we're still inside debugger so we can walk through that. So the catch is going to run and then our finally is going to run. And notice that it's output are displayed to the console. So our error there got output. There's also more advanced ways of passing those errors up and so let me show you what I mean by that. So for example I could take and inside of the catch I could actually throw another error. So what I could just do is type in throw e. And have this return our variable here again. So we've got our try and then in our catch we're throwing the error. So what throw means is throw the error back up to the calling function. So what I can do up here again is do another try catch. And let's run this this time. I'll go ahead and clear our console so that we start fresh. And so again it just outputs null. And we see our error display that gets pushed. Let's go ahead and walk through this into bug error so we can see what's happening. So we set our variable we start walking through this and we hit an error immediately. And we take that error and we throw it back up to the calling method. So it comes into the catch block and runs that code. And so that's how you can have your own functions that you're writing return back. Their own sort of error messages to the calling functions. Next let's take a look at a different way of error handling. So we've discussed general JavaScript error handling. Let's take a look at some other types of errors that may happen in your applications. Specifically maybe some database or servoy specific errors. So if I click on my solution I can see that there's an on error function here. So I can specify a global method to run whenever an error happens in my entire solution. So I can click on the on error and I can create a global method. And we'll just call it on error. And if I open that up I can see that it's actually created a nice block of sample code for me. So currently we're actually taking in the error as the initial argument and then we're going through and figuring out what type of error that is. And we're doing that using the servoy exception note. So down here you can see some information like get the error code, get the error message and you can compare those things to see exactly what type of error it is. So here we're checking to see if the error is an instance of a servoy exception. So let's just go ahead and run this. You can actually see real world example of what happens here. And actually what we'll do first is we'll put a line break on that. So let's go ahead and run this and what I'm going to do is make a new record. And I'm not going to type in an ID value. This table actually requires you to type in an ID but I'm going to leave that empty. And I'll click out here and because the ID value is empty you can see an error has been thrown. And so let's walk through this new bugger. So we can type in E here and we can see that that's an application exception. And we're just going to walk through this. And so we just output some general information about the error. We check to see if it's a servoy exception and it is. We have output some more information about the servoy exception and actually get the specific error code. And it is actually a database save error. And if I come back over here, you can see the error popped up. It says it seems like you did not fill in a required field. And I can say, okay to that and then it brings me back here. So I can start walking through that. So now that we know that it was actually a database save error, we're going to walk through and get some information about those records which failed. And output some information about why they failed. So I can come back here and we're left waiting for me to type something in here. So it'll require me to type something in before it'll let that save. And still it looks like I didn't fill in a required field. So let's try a company name. That's better. So we need both company ID and company name to get that to work. Now let's compare that to what would happen if I didn't have a global solution on error method. So what I'm going to do is go back to my form here. And let's go to my solution and I'm going to take that on air off. So we'll save that and we'll run it again. So now when I try to create a new record and I click out, you see I'm just getting the default cannot save form data message. So by using the global solution on error method, you're able to trap all these sort of errors. And instead of displaying the servoy default message, you really get full control over that.