All language subtitles for 002 Understanding _let_ and _const__en

Let's dive right into it with let and const. These are two keywords you're going to see a lot in this

course, especially const. Let and const are different ways of creating variables.

You know var, var creates a variable in javascript.

Now the thing is some variables never really change,

They are so-called constants.

Technically though, they are.

They are all just variables because javascript only knows var. With ES6, a version of javascript, two different

keywords were introduced, let and const. Var still works but you're highly encouraged to use let and const

Let is

so to say the new var, you use it for variable values. Let and const are all to changing something behind the

scenes about the scope of variables.

But the most important takeaway here is use let if you want to create a variable that really is variable.

Use const if you plan on creating a constant value, so something which you only assign once and never

change.

And that is the case more often than you might think.

In this course you will never see var, you will only see let and const and mostly it's const. So it

shouldn't confuse you,

It's simply the same as var, just in a more modern way, and in the case of const, although clearly

showing, this is never going to receive a new value.

Now since this is always a bit clearer in practice let's have a look at it. For this,

It's best if you use jsbin

.com,

That's another web editor which makes it easy for us to enter some javascript and see some console output

for that, disable HTML and output up there and instead to enable Javascript and console.

Now on the left side you can right next generation javascript, on the right side you'll see the output.

So there we can create a variable.

My name, set an equal to Max, console log my name, now hit control enter you'll see Max on

the right,

Not that new to you probably.

Obviously we can then set my name to Manu and if we then console log my name again.

It might also not totally surprise you that if you clear and run this again you'll see Max

From the first statement and Manu from the second one.

Now if you change var to let,

Nothing's going to change.

Hitting run still works the exact same way. If you use const though like this.

Then clearing and running this will output Max,

But then throw an error, since we try to reassign a constant variable which is kind of a strange name.

This is const and this is the idea behind const.

You can say this should never get a new value and if you then accidentally write some code where you

reassign it you get the error and hence a chance to improve your code.