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We'll come back to lesson six, null and undefined, this means no is it intentionally points to a non-existent

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or invalid object address.

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Think of a room that explicitly has been marked as empty.

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And then undefined is a little bit different, that's assigned to a variable that was just created,

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just declared, but no value has been assigned to it yet.

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So it's not explicitly empty.

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It's as if there is no room there.

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So it's kind of the difference between having a room that's, you know, is empty and having a room

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that you haven't visited yet.

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So you don't know what's in it.

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So we're going to look at these in code and learn a little bit more about them.

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OK, so here we are and there's not a ton to get into right here, but basically we can.

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Just do some sample variables and let's just say we declare this variable, variable one.

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Now, if we just go ahead and cast a long time,

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then we're not going to get a specific value.

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What we are going to get, though, is this value undefined?

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It's not necessarily a problem that a variable is undefined.

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It's OK if it doesn't have a value, certain variable types.

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It's not OK if they don't have a value.

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So const, for example, it's going to shout at you, hey, since you're not going to be able to edit

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this value later, you need to initialize some value in this declaration so you're not going to find

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const variables that are undefined.

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But we could set this to know if we wanted to.

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We totally could and give it in no value.

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So that means it's explicitly empty.

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What's fantastic about this is now we have a variable that is always going to be No.

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Very interesting.

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So since we can't reassign it to any other thing, right.

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Remember how we can't give this a separate value later because it will catch us and be like, hey,

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you cannot assigned to a constant variable, stop that.

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So we're better off just like that.

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And we have null and undefined.

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So in computer science and no value is it represents a reference that points intentionally to a non-existent

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or invalid address, so that varies among languages.

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But basically here we're just saying this has no value, which if you interpret this as a true or false

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value, it is false.

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OK, it's fairly primitive, but as far as it being a primitive data type like numbers and strings,

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but there are other things that you can do with this involving objects, and we'll learn about those

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later as well.

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Now, undefined, if you recall from this other example, you can't do it.

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So let's do let.

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So if we just set this up and just give it no value, we just declared it, but we did not sign anything.

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It is undefined.

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OK, so this comes in handy when we need to calculate the variable value later or if the value is dependent

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on the user's input so we can just create a variable now and use it later.

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So we'll see later on.

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We want to reset the value to some user information.

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So we'll just we'll just prompt for for some value.

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And then we see a.

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And then we could on that as well at the end.

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So let's say, hey, and there you go, the prompt spat out, the answer to that prompt prompt is a

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really cool thing.

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You can as you can see, you can use it to just make a little quiz question anywhere you want.

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Prompts are used a lot for authentication on websites.

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Hey, you need to log in, put your password in things like that.

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Just built right into JavaScript is very basic, basic function, as you can see.

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OK, that is it for null and undefined.

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And we will come back to you to.