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In production we don't want to have any of
these errors or

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exceptions being displayed to the user,
but we do need to report these errors and

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other information somewhere.

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What we want here is logging.

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The idea of logging is very similar to how
most errors work.

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Most general logging systems have common
efforts like debug,

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info, notice, warning, error, and
emergency.

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PSR-3 was developed to standardize the
interfaces for basic logging interactions.

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By itself PSR-3 is just a set of rules and
interfaces.

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So we need to use an actual logging system
that implements PSR-3.

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One great logging system is called
Monolog.

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So, first things first, let's install
Monolog Fire composer.

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We can use our console to type composer
require monolog/monolog.

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I'm gonna ask for a version.

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You can use tilde 1:10 to say we accept
1:10 or above.

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There.
Now it's installed.

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We won't need our console any more in this
lesson.

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Now we can open up index.php and take a
look at how we use Monolog.

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This is an example of using Monolog in a
fairly procedural code base.

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Again, this is not really represents
different higher applications should look.

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Really they should be split up into
logical files.

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But it does show us how we can get Monolog
to log stuff quite easily.

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So on line three here we're including the
composer auto-loader which will

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help us load our monolog code.

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Down here we're referencing the monolog
logger in a use statement.

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This will make logger available in the
global space.

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In line six we're bringing another class
into the global space and

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this time we're taking the
BrowserConsoleHandler.

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Monolog uses the term handler to mean,

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a class which decides how logs should be
sent out to various locations.

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There are a lot of different handlers for

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sending things to lots of different
places.

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Such as, outputting to different log
files, sys log, the browser console,

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emails, or even hosted logging providers
like Logly or New Relic.

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Now that various classes are available we
can instantiate our logger class.

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We pass a string to the constructor as a
first argument and

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this is the name of our logger.

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This can be anything you like and it's
just generally a name to help you

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differentiate logs because multiple logs
can be sent to the same location.

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The logger instance is then stored in the
log variable so

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we can work with it further.

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After we set up our login, we then want to
set up our handlers.

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So we use the pushHandler method to add in
instances of various different handlers.

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Here, we're only adding one handler to the
log.

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But really, you can add multiple for all
sorts of different things.

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We're only using the
BrowserConsoleHandler.

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And you basically use that by creating a
new instance and

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sending it to the handler.

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So, enough of me reading code.

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Let's have a little go and see how Monolog
works.

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So, first of all, log, everything is
reference from the log variable from here.

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You can run messages like error or
warning.

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We're gonna start off with some debug.

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Now this method is provided by the PSR-3.

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So if you use debug, and error, and
warning, and

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things like that, then they are definitely
always gonna stay the same.

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Know they work as they take the string and
you can say something is happening.

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It doesn't have to be a big scary thing
it's just letting you know that

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something is happening.

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So now if we open up our preview we can
see how this all works.

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If we open up our browser console in
Chrome or pretty much whatever else you're

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using then you'll see here in the console
tab my app, debug, something is happening.

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This means our messages are coming
through.

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Let's get a little bit more adventurous.

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Maybe we're trying to debug something
that's happening in a loop.

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And just to make a really simple little
loop here.

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Let's just make this loop through ten
times, and we'll call it foo.

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We can put that down on a new line, four
spaces.

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Okay, let's save that.

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So here we can see the something is

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happening message appearing ten different
times.

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Now this may or may not be useful.

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What would be even more useful is if we
could pass a context to these messages.

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So we can make an array.

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This is the short array syntax if you're
not familiar.

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And we can say it's an associative array,
so

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pass it a name and then pass it a value.

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We turn back to our preview.

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We can see that we've got these little
carrots and these provide context.

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You can put as many different variables in
there as you want.

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So as well as debug we have warning and we
have error.

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[BLANK_AUDIO]

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We even have critical.

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You probably want critical to send an
email to the CEO or something.

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Like these critical errors, or any use
that's super bad.

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So, let's make that message appropriate.

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Now if we refresh,

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we can see there's a whole bunch of debug
information happening.

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There's a warning, there's an error, and

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there's a critical error right at the
bottom here.

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Now, something we might want to do,

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depending on the type of handler we're
using, and

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how many different handlers we have.

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As you might limit which items go in which
log.

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To do this we can send an extra argument
to the handlers and

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this argument is a constant supplied by
the logger class.

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I'll show you what that means.

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You go to the browser consort handler and
you use logger to access a constant.

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By passing it the warning constant we're
saying we only want something that's

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a warning or higher.

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To get back to preview take a look.

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Now we've only got our warning, our error,
and our critical.

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We only want errors and above.

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Excellent, and of course.

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And there we go.

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You'll want to play around with the
configuration of which handlers and

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which reporting levels to use.

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But that is the beauty of a logger like
this.

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No matter what types of handlers you use
you only need to change those

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handler set up lines and know the part of
your application.

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There's an extra benefit to Monolog being
PSL 3 compliant.

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If you want to use another logger system
there is a good chance that,

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that system is PSL 3 compliant too.

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If they are both compliant, once again,

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only the setup code in your application
will need to change.

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Your entire application can rely on the
logger by passing the log

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instance around in service locators or by
passing it into other classes manually.

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Knowing it'll be PSR-3, you don't have to
worry about changing any of

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the methods your logs use because they'll
always be the same.

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That's it for this course.

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I hope you've learned a lot about
standards and best practices.

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My name is Phil Sturgeon, and you can
reach me at philsturgeon.uk or

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@philsturgeon on Twitter.