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Now we are on Section three coding basics, so we're going to get past the environment that we learned

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about in Section two, the history of JavaScript, into a lot of actual coding now.

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So first things first, Section three.

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Lesson one is about the execution context.

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This is more of an abstract idea.

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So we're not going to learn a whole lot of code in this lesson.

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The whole purpose of this lesson is to understand how JavaScript runs.

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And really, it's just the idea that whenever any code is run in JavaScript, it's run inside a specific

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execution context.

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So there are three that we'll learn about.

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There's the global execution context, the functional execution context and the evil execution context.

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So let's take a look at those in code.

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So we've looked at this before.

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We're looking at the example from the end of our coding challenge from section to.

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And we have a global execution context in this script that basically refers to anything that is set

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up and run at the highest level of the code.

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For example, this variable declaration right here, MSgt for message.

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This is run at the global execution level.

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There is also a function which is defined globally.

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But then the contents of this function are inside of another code block, and these are running in a

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functional execution context, that just means that they are running inside the function.

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And the purpose of execution context is more of a memory usage.

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So it's just saying that this is its own script within a script is what functions are.

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So it's a block of code that's going to run inside of this other larger script.

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So it's like.

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The global execution context is running on top of that, you may have a function that runs.

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And that it would be a second execution context and then a third execution context is eval.

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So evil, basically, you can use to evaluate JavaScript code and execute it.

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It's not recommended that we use this anymore.

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But you can it's not nobody's going to slap your wrist, but definitely it's something that is deprecated,

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mostly replaces functionality, better functionality that we use in the general context.

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So I would recommend not using eval.

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It's not necessary to run your proper code.

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And the reason it's not preferred is that because it runs in its own execution context, it runs its

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own set of memory.

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So it uses memory on your computer.

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And it does so with less efficiency than the global execution context and the functional execution context.

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So we can refresh this and it will execute that code for us and it will do it inside its own context,

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but generally it's understood that, you know, we don't prefer to use eval, OK?

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So we're going to go ahead and comment that out.

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And make a note here as well.

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Eval is not preferred in its six plus, which is the current version of JavaScript.

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OK, so that's pretty much it for lesson one, the execution context.

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We just wanted to show you the difference between the global execution context, where anything happens

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at this top level, the functional execution context, where anything inside a function will run it

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in its own process.

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And then this no longer used evil process, which you can use to run code in its own context as well.

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OK.

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How the order of these operations happened, when it's running the script, it will run the global context

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first, then it will run any functions.

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And if it has any events, it will run those as well.

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OK, that's it for lesson one on to listen to and to listen to.

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We're going to be talking about single line and multiline commenting and type coercion and variable

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mutation.

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OK, see you soon.