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[MUSIC]

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As you may have already noticed, our apps
are bound to have some errors, whether

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it's code, we've written or changes in
the resources and dependencies we use.

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Thanks to the Error object.

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We can get feedback from errors occur and
this helps us correct them.

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Think about a math test for example, if
you handed in a math test, and the teacher

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only returns the test back to students who
got a perfect score, that's not helpful.

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If you hand in the test, and the teacher
marked which question you got wrong,

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that's somewhat helpful.

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If you handed in a test in the teacher
indicating not only which question you got

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wrong but
indicating what type of mistake you made.

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Maybe you forgot to carry the three.

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That's something you can learn from,
done right.

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A JavaScript error handling can
function like a great math teacher.

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They can tell you not only where
your code stopped working, but

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also what type of issue
caused the problem.

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There are different types of errors that
can occur in node, and these include

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standard JavaScript errors, system errors,
user specified errors and assertions.

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Were able to find out
more about a given error,

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including its type by
examining its properties.

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These include the error stack,

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which describes when
the error occurred in the code.

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The error code, which tells us what
kind of error, there's a great list in

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the documentation and the error message,
which is a string describing the error.

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One method of error handling you might
be familiar with is the try-catch block.

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try-catch block is an error handling
technique used to execute a block

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of code and

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throw an error message if something goes
wrong within the block to be executed.

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These are useful in JavaScript, but
with many of Node's asynchronous methods,

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the try-catch block is executed completely
before Node.js methods have a chance to

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finish.

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Because Node.js is asynchronous in nature,

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we will handle most errors in
Node using asynchronous methods.

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Let's intentionally create
an error in our project,

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we remove the period from URL and
then save, and try to run our code.

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We get a long error message that may be 
difficult for app users to interpret.

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The error messages includes
the code ENOTFOUND.

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We can look this up in the node
error documentation and

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find out if this is a result of
the address not being found.

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Which makes sense for
an address that doesn't exist.

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We can use the tools that node gives us to
handle this error in a more user friendly,

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organized way.

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An incorrect but valid URL in the
asynchronous block of code won't be caught

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by something like a try catch block.

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It's not until runtime or
the code is executed and

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the async call starts, that this
error will be recognized.

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Just like we watch for data in events
earlier, we can watch for errors as well.

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On the request object we will
watch for events with on.

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Watch out for the error event.

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Give this a callback function
that takes the error.

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And will use the console.error
method to print out the error.

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I will save and will try it again and
this has removed some of the extra text,

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but we can go even further and
narrow down specific properties

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of the Error object. Let's go with
the error code for example.

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There we go.

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Now many users may not know
what these codes mean.

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We can write a custom error
message in this handler as well.

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There is our custom message.

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Now, a bad argument,

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like removing the HTTPS protocol
will cause an error right away.

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When we remove the protocol from our URL,

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Add the period back,
save, try running again.

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We get an invalid URL error.

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This is caused by a missing protocol or
invalid URL.

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The asynchronous call cannot be made
without the correct protocol so

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this error is synchronous.

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In this instance, the program will
be unable to continue running.

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Because of this, it is a rare case where
we can use a try-catch block in Node.

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We'll wrap the request in a try block.

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We'll catch the error, and

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use console.error again to
log out the error message,

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And there we have it only
the error message appears.

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We can again customize this even
further to make the message our own.

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Great work, in the next video we'll
look more at the try-catch block for

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parsing errors.