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This lesson we're going to be looking at function scope, so go global scope of variables and values

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and local scope of variables and values.

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So they're really the difference between the scope is where the value of the variable is declared.

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So you see in this case that we've got a variable rate and we've called it Tarlow and then we've got

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variable B what this what this one is only living within the function so we can console logout E plus

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B while we're in the function.

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So we invoke the function and everything is great.

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We'll see.

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Hello World.

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But then when we do console log B and this is trying to get a variable that lives within the function

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and we're not able to access it because we see B is not defined.

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So the thing that is happening here is this is having to do with the scope of the variables.

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So the way that variables work and within functions, you can access the value only within the block

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of code or its parent.

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So if this particular variable is not declared and we've got our root scope here, so the AI is on the

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root and we're trying to look for B on the root as well.

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And the reason we're not able to find B is that it's not on the root and it's not on the parent and

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the root doesn't have a parent.

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So that's why we're not able to find any value for B, whereas within the function we look for B and

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then we've got Consolo A plus B, so JavaScript first looks for this block of code within the function

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and it sees no end there.

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So it automatically reverts back to the parent and it looks for that same variable being defined within

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the parent.

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And if we had another parent and another parent, it would continuously look into the parents until

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it actually found that variable.

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And if the variable was not there, then it would still show us that undefined.

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So that's how the scope works.

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And I'll give you a quick example of that and the way that that can work.

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So if we set up a variable and we've got a value of five, four, eight, and then within test, we

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can console log out a and then we invoke test, you can see that the value of A gets placed within the

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function.

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Now what happens if we take a and if we redeclared it only within the function itself.

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And remember, we're still outputting a within the console.

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So this actually leads to two different A's.

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And as mentioned earlier, the way that JavaScript will work is it will look for a within the current

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block.

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And if it finds it, then it will use this value of a.

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So even if we try to get a value of a before we declare it, we see that it's not declared because it

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doesn't go to the parent.

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It knows that we've got a value of a that is within this block, but we know that it isn't declared

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first.

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So we need to declare it first before we try to use it.

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And that's why we're throwing that error.

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So if we comment that out, then what happens?

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JavaScript goes through, invokes the function and sees that there's no E available within this block,

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a code that's being declared and it will revert back to the parent.

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So go ahead and try this out.

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And it does take some getting used to so you can try to declare various variables, declare some variables

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within a function and then use them within your code.