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24.9
Yep.
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0.5
So repeating for the camera, line 25, thisIsHoisted is declared as a constant
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so it cannot be changed, whereas line 21 is declared as a function and so it can
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be changed, which is absolutely correct.
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What happens if I try to do this up here?
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Yeah, so we're going to get an error.
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thisIsHoisted is not defined, but why?
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Because as we talked about earlier, these things
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called consts are not available for use until they're actually declared.
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So certain things are hoisted.
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Var.
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So the declaration of these variables are hoisted.
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Function definitions if they're declared like this are hoisted.
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But if we create what's called an anonymous function,
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a function without any name, and set that equal to--
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or assign that to be a constant, then that constant is not created.
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Does that make sense?
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So what happens if I try to do this?
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Yeah, so same thing.
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It errors.
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3.06
What happens if I try to do this?
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What's hoisted?
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0.625
So notice-- so notice the difference in the two errors.
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They're actually not the exact same error.
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So who wants to give a guess at what's going on here?
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So when I declared it with a let that's saying reference error,
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thisIsHoisted is not defined, whereas when I use a var,
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it says TypeError, thisIsHoisted is not a function.
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Why might that be?
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Yeah?
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Uh huh.
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Exactly.
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So repeating for the camera., and I'll bring up the code as well.
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So down here, so the first time when we declared this with the let,
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it's not declared at all.
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This variable does not exist at all.
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So this is not hoisted, the JavaScript does not
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know what that means on line 1.
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But when I use a var here, remember, it hoists
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the declaration of this variable.
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So it creates a variable called thisIsHoisted.
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However, it does not assign it a value until line 25 is executed.
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And so at line 1, thisIsHoisted exists.
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It's just equal to undefined.
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And if I try to invoke it like a function,
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it says, hey, this is an undefined variable,
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I can't invoke it like a function, this is a TypeError.
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And so even though both of these things errored, the reason that they errored
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is slightly different.
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In case one when they're declared using a const or a let,
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that variable just does not exist at all.
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However, when we declared using var, the variable exists.
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It's just undefined, and so if we try to invoke it like a function,
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and it says, hey, like, this is undefined, it's not a function.
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Does that make sense to everyone?
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So why does this happen?
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How does this happen?
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And the reason is actually how JavaScript is executed.
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So there's two phases in the execution of a JavaScript file.
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So before executing any code, it has all of the text in front of it,
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but it hasn't executed anything, it just reads the entire file.
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And what's it looking for?
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Well one, it's looking for anything wrong with the file.
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So say like my very first example when I had an array and it was missing
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a comma, that's something that's caught in the first reading.
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It says, hey, like, this looks like an array but it's not quite right.
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Like, I see this thing that I'm not expecting, I'm respecting a comma here.
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So that's one thing that's caught.
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Other things, maybe it will add some semi-colons for you
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and stuff like that.
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And then any function definitions just get saved in memory.
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It says, hey, this is a function, let's put this in memory
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so if somebody wants to use it at line 1 they're able to.
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Variable initializations, if they're lexically scope-- or I mean,
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if they're lexically-scoped they will be declared,
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but they will not be initialized.
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Meaning anything declared with var will be
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declared-- like there's a variable that exists,
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but it's not going to be set equal to anything until later.
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And then there's a second phase called the execution phase, whereby the code
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is actually run, it's executed.
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And so that is when things like const or let get invoked--
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or get both declared and initialized.
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Does that make sense to everyone?
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Anybody have any questions on scope?
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So why might we take advantage of this scoping?
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Does it seem like a feature or does it seem like a bug?
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Anybody care to guess?
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There's no correct answer to this.
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It's completely opinion.
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Yeah?
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AUDIENCE: So you've got a controller with math functions in it.
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JORDAN: Uh huh.
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AUDIENCE: You can call the ones there and lay down
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a file so that you can write all your code in one giant function?
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JORDAN: Yes So, one thing might be we can
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have these function declarations at the very bottom
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and then we can use it at the top.
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And so that might be good for code organization.
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Like somebody reading your code would know, hey,
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