WEBVTT

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In this chapter you're going to learn new ways of declaring variables in E6 and how this would affect

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scope and hoisting.

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Now before we dive in let's have a quick review of the year fives var declaration its scope and hoisting

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so

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in is 5.

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We used to declare variables using var mainly we had also concerts but we're gonna come back to concerts

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later.

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So let's declare a variable X and set it to 1.

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Now I'm a variable x is gonna be global scoped because we are declaring it in the global scope outside

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any function.

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Now we know that variables were global scoped or function scoped.

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So if you declare a variable or a function at 1 for example and you declare a variable X inside it then

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you know that this variable here is a function scoped unlike the first one which is global script.

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Now if you return something like Y plus X and you try and one of three then you know you're gonna get

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s 5.

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And that's because when you get there and you look for the value of X first of all you look for the

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value of x inside the execution context of your function and that's where you find X equal to 2 right

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there and you use the value to.

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Now if you create another function and 2 and you do not declare a variable X inside a 2 and you try

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to 0 3 then you're gonna get 4.

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And that's because when you get away that and you look for the value of x inside the execution context

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of your function are two you don't find it.

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Then you go to the outer environments of the function or its execution context and you find X in the

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global scope and then you use the value 1.

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And that's why you get 4 which is 3 plus 1.

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Finally we know that variables in is 5 were hoisted

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when you declared them using 1.

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So if you log for example a variable Z before you declare it you wouldn't get an error while you get

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undefined.

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And the reason why is because all the variables declared using var they are hoisted at the beginning

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before the execution of you of your code.

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So before you code gets executed you know that z is going to be hoisted and set to undefined.

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Now when you get to that line

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you haven't said Z yet.

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So you're gonna use the value undefined which was set to when it was hoisted so no error.

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Thanks to hoisting now if you log Z at the end you're gonna get one this time.

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So this was a quick overview of the.

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Var declaration.

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It's the scope and hoisting in Ian's wife.