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Welcome back.

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We're now on lesson two of Section three, single line and multiline commenting type coercion and variable

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mutation.

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First thing, we're going to talk about a single line and multiline comments and then we'll come back

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to this and talk about coercion and variable mutation.

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It's best practice to use comments frequently to document your code.

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It's also extremely useful for commenting about code you're not sure is working properly or to test

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various versions.

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So let's take a look at our code.

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So as you recall from our last lesson, we looked at this example of the global execution context.

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So how could we document this further?

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How could we do a better job explaining this here and cleaning this up?

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OK, so let's make sure this is going to the right one.

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So one thing we could do is add a single line comment and the way we do that is with two forward slashes.

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And you could also do a controlled forward slash toggle between comments and not comments.

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And we could explain this is the global execution context, so this is a form of documentation context

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so we can explain to the reader of this code what we're trying to explain here.

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And then we could jump in here and say.

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Function, execution context.

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OK, and we can go down here and instead of having these two lines, which they're really kind of sequential,

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let's do a multiline comment.

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So the way we do multiline comments is with a forward slash asterisk and then we can say eval execution

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context.

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And then when we have multiline comments, we don't actually need to have the original double line comments

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anymore, we just need to end it with one of those.

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And so these could be just on their own separate lines.

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Multiline comments are nice, especially when you have a long paragraph that you want to document,

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some people would like to do this with multiline comments just so that all the lines are indented to

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the same degree.

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Definitely up to you.

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But the purpose here would be to.

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Comment something out that is multiple lines, and especially for documentation purposes, if you have

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a long paragraph that you'd like to comment out and break it down into multiple lines, you can certainly

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do so with a multiline comment.

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So that's a forward slash asterisk and end it with an asterisk forward slash.

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So that's how you do it.

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There's a very similar process that works in HTML as well with a multiline comment.

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OK, so that is single line commenting and multiline commenting and what's nice about single line commenting

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is it's easy to toggle those on and off to test individual lines of code.

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But now let's get into the next section of this, which is type coercion.

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So let's learn about type coercion.

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Now, the purpose of coercion is just that JavaScript automatically converts numbers and booleans to

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strings during concatenation with the plus operator and strings.

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That's a lot of information.

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Let's take that piece by piece.

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OK, JavaScript is going to automatically turn numbers and true or false values into text during the

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process of adding these pieces of information together in a line of text.

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OK, so let's look at an example.

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Now, the reason this is important to note is that we need to understand that certain pieces of data

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are just going to be read and understood a little bit differently depending on the way that they're

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used.

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So let's start with.

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Let and let's just set up these three variables, OK, and what's happening here is something called

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declaration.

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We're going to get into that in the next lesson a little bit more.

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We just did a declaration of multiple variables.

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Now we're going to assign them some values.

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So let's just see.

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This animal is a dog and let's do is hungry.

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OK, make sure that you're using the same variable names that you've already set up, if you have a

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typo, it's not going to understand it.

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And of this new age equals 12.

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OK, so as you can see, we have three variables here.

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Animal is hungry and age.

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And with this one noticed that the second word has an uppercase letter, this is called Camil Case,

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and it's just a very nice way to be able to read a variable name that has multiple words in it.

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So this is a standard across a lot of programming languages.

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There are other ways to make variables easy to read if they have multiple words like snake case.

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Which is like that.

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Kabab case, which is like that, but the preferred way for variable names in JavaScript is camel camel

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case like this.

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OK, so we've got these three variables.

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We've assigned values to them and notice that this one looks different than this one and looks different

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than that one.

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That's because this is a string and this is a boolean, which means it's a true or false value and this

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one is a number.

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So obviously, this looks like a line of text.

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It's in quotes.

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This looks like a number.

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And this looks like it's not exactly the same as this.

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It's not a line of text as understood by JavaScript.

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It's not a string.

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It's a special keyword that indicates that something is true.

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So this type coersion right now that we're going to get into is to show you what happens when we automatically

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push these together.

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So let's console log.

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My.

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And then we use the plus to concatenate concatenation means we're going to glue multiple texts together

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and then we don't need to put the variable in quotes, we just say the name of the variable and that's

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going to execute or invoke that variable.

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And then we do is.

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So so far, what is that going to say that's going to say?

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My dog is.

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Let's add.

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Age and then add years old.

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Now, one thing I got to make sure of is that I have spaces in here because it's not going to add the

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spaces automatically for me.

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OK, so now we've got spaces and then let's add.

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OK, so we went ahead and saved that and let's test it out.

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My dog is 12 years old, so interesting just to note that even though 12 is a number, it changed,

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it coerced, so it forced.

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The number 12 to be understood as a different type, so the string is one type booleans and other type

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numbers, another type, so we can actually force a Boolean to act like a string or force a number to

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act like a string if we can cat need it in strings so we can actually cancel log.

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We could do if.

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If is hungry.

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Then council log.

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My.

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Animal is.

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Hungry?

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So we have this conditional expression happening right here where we're saying, if my dog is hungry.

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Then print out, my dog is hungry, is hungry, is true, OK, in this case it is true.

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So it should print out to the console.

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My dog is hungry.

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And there you go.

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It worked, my dog is 12 years old and my dog is hungry, so that's what we did to coerce the type of

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12th and true to be acting as.

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So let's just test to see what happens.

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If we say our dog is hungry, we could say it's

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true.

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He's hungry.

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OK, so now we're going to see what happens when we refresh.

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So because it is hungry, we made this conditional expression in this if statement and said, if hungry

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is true, then council log, it's plus true.

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Plus, he's hungry.

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So it turned out is true right here, which is a special word, it's not a string into a string because

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we can cat needed with strings.

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All right, so that is type coersion.

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Variable mutation is the simple idea that you can take this and change the value.

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Now, if I want my age to be 13, I could do that.

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And that is the variable

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mutation.

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And if I change is hungry.

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To false.

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Now, if I try to run this again.

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Do you expect it to run a second time?

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Let's see.

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Now, it only ran once.

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In fact, if I come at this one out, just so you can see.

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It doesn't run at all because now Hungary is false, so it does not meet the conditional expression

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required to run this line of code.

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So that is it for our review of single line comments, multiline comments, type coersion.

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And variable mutation.

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And we'll see you in the next video, we're going to talk a lot more about what variables are the different

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versions of variables and how we can make those work.