All language subtitles for 32 - Activating Strict Mode English

Now before continuing to learn JavaScript,

in this new section,

we should first activate a special mode in JavaScript,

called Strict Mode.

And here on my desktop I already have the folder,

for this part 2 fundamental section.

And for you as I explained before,

these starred files come from the get up repertory

that I showed you at the beginning of the course.

So use that get up reparatory as your starter folder

or ofcourse you can just copy that data

somewhere else to your computer and work from there,

whatever works for you.

Now I'm creating here in UVS code window

and lets open this new folder.

So that's our new working folder

and this time we already have the script file here

and in the HDML file,

we see that the script is also already linked,

so we don't have to do that this time.

At this point I assume that you already know how to do that.

So closing the side bar here

and lets now get started in this new section.

And as I said lets start with strict mode.

So strict mode is a special mode

that we can activate in JavaScript,

which makes it easier for us

to write a secure JavaScript code.

And all we have to do to activate strict mode

is to write this ring at the beginning of the script

so use strict and that's it.

So with this, we activated strict mode

for the entire script.

Now what's important is that this line of code,

so this statement here basically

has to be the very first statement in the script.

So if we have any code before this

then strict mode will not be activated.

Comments are allowed because JavaScript

will just ignore them but no code.

Okay, now we actually can also activate strict mode,

only for a specific function or a specific block.

But I don't really see the point in doing that

and so I always just use it at the beginning of each script

and so I believe that you should do the same.

So always just put strict mode

in the beginning of your scripts

and like that write more secure code.

And when secure, I mean that strict mode

makes it easier for us developers

to avoid accidental errors.

So basically it helps us introduce the bugs into our code

and that's because of 2 reasons.

First, strict mode forbids us to do certain things

and second, it will actually create visible errors for us

in certain situations in which without strict mode

JavaScript will simply fail silently

without letting us know that we did a mistake.

Okay.

So again, first strict mode forbids us to do certain things

and second it creates visible errors

and the developer console, where in other situations

JavaScript would just fail silently.

Okay, but now to make this a bit more clear,

Lets actually see an example of

one of the most important changes

that strict mode introduces.

So lets create a variable here

with a complicated name lets say hasDriverslicense

and lets initialize it as false here.

And then I'll also create, pass test and set that to true.

And I'm using let in both of them

because I want to change them later

and actually this one not.

So lets just use a const here,

because remember by default we should always const

to avoid accidental errors.

So basically there is a certain person

which right now does not have a drivers license

but they just passed a test,

that's why we have passed test set to true.

And now we want to write some logic

so that when they pass the test

this variable here gets set to true.

So, we can say if passTest, right?

Because this one here is a boolean value

and so this condition will be either true or false.

And then lets introduce a simple bug here, okay?

So this is a kind of hard to write variable name

and so lets pretend that we are writing it wrong here.

So hasDriversLicense equal to true.

So what I did here was to basically omit the 's'

So this letter here is not in this variable

that am trying to change here to true.

And again that is an error I'm making here on purpose,

just to show you how strict mode can help us

avoid a certain kind of error,

because doing this is actually more common

than you might think, okay?

And now lets lock something to the console

if the person has the drivers license.

And so now were actually gonna go back

to writing it correctly.

So if hasDriversLicense and so you see that now

this one is exactly the same,

as VS code highlights both.

So if hasDriversLicense then log to the console,

I can drive.

And now lets actually start

by deactivating strict mode again,

just so we see how this bug could affect our code.

So I'm giving it a save and then lets go

and open this index.hdml file.

Okay?

Now lets open up to console here

and again I'm gonna increase the text

by hitting command plus a couple of times here.

Okay?

So lets reload here just to make sure

that everything is working

and now what we see is that it didn't log I can drive

to the console.

Even though we had attempted to set

hasDriversLicense to true here,

so we expected that drivers license being true

should then log I can drive.

But it didn't work and that's because of the mistake

that I just introduced here on purpose

forgetting this 's'

so without the error it should work, right?

But without it, its not gonna work.

And again because basically here

I set a new variable to true

and not the original one,

so this one is still false

and that's why here, this logging does not happen.

So now our program has a bug

which means that it has a mistake

and we would now go ahead and find that bug.

But, strict mode can actually help us with this.

So lets turn it back on,

give it a save, now try it again.

And now we actually get an error.

So here we see that hasDriversLicense is not defined,

so in line number 6 which is right here

and so this error message now tells us

exactly what is wrong.

So it tells us that this variable is not defined

and then we can see, oh we did a mistake here,

we're missing the 's',

right, so now its the same variable,

here, here and here, okay?

And so if we try that now again.

then the error is gone.

And so strict mode really helped us avoid this kind of bug

that we created here.

You can experiment a little bit with this

to make it really clear.

Now another thing that strict mode does

is to introduce a short list of variable names

that are reserved for features

that might be added to the language a bit later.

For example, lets try to define a variable called interface,

for example, for an audio interface

and now if we try this.

Then we see that, we get an unexpected strict mode

reserved word, error message basically

and that is again because JavaScript

is reserving this word here for a feature

that it might implement in the future.

And so by reserving these kind of words

it will then make it easier

to implement the feature in the future.

So another one is private for example,

so const private, just some number here

and so this one will also not work.

And that's because in the future

there might be something called a private field and classes

or in some other places even in the language

and they might want to use this word for that.

And so strict mode reserves these words

so we cannot use them for variables.

It's the same logic as this one

so we cannot call a variable 'if'.

Right?

And that's because there's already an if statement.

So here we get an unexpected token 'if'

so that's like the rules

that I explained to you in the beginning

about naming variables.

Okay? Alright.

Now there are actually a lot of other changes

that affect things that we haven't learned about yet.

So, that's stuff like functions, objects,

setting properties on primitive values and many more.

And I will mention them in future lectures

when the time comes.

But everything that I'm gonna say

in the rest of the course from now on

we'll always assume that you have strict mode turned on.

And so I will add this line of code here

to all the scripts in the future

and so you should do the same.

Anyway with this out of the way

lets now start learning functions.