WEBVTT

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In previous lecture, you have introduced what the execution context is, so it's like a container that

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managed the code that is currently running and when something is running your brother, execution context

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is created.

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And at the same time, JavaScript engine prepares the environment for execution JavaScript code.

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Let's take a look on the screen and see together how it actually happens when a stimulus package is

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loaded in a Web browser, even without link for JavaScript file, the engine prepares the environment

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for running JavaScript code.

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At this time, the global execution context is created, which we have not discussed yet up until this

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point.

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So what is that?

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Global execution context is a base execution context that manages the code, which is not inside a function,

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and it is created immediately when the page is loaded.

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So the global execution context managed when the cold execution starts and ends and you will see deeper

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incoming videos before it actually starts to execute the code, it creates global object, which is

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the same as window object.

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A global object is an object that always exists in the global scope and simultaneously there is created

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a special keyword of this, which is equal to global object at the global level.

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I know that all this stuff sounds a little bit confusing.

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Therefore, I'm going to use some practical examples.

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Let's go back to your text.

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Ed, I want to show you something.

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You have our empty script, dodgiest file.

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Now let's go to index, not HTML, and post the link between index, e-mail and script digest files

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commented out.

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So it means that we have no longer connection with JS file.

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And as we said, the engine prepares the environment for run the codes.

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Even without loading JavaScript file.

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We can prove that.

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Now you remember that once we have used a method from document object model in previous videos, this

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method allows us to access on elements.

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I mean, document out that element by ID.

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So let's at first assigned the idea attribute for H1 element and call it header.

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Then use the immersion method and writing council document.

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Douget 11 by IID, then right here, the idea of the H1 element header and then use the property in

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her e-mail.

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So you see that we have content of one element.

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It means that everything is prepared in browser in order to run and execute JavaScript code.

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All right, let's type in console or window, as we said, one, the global execution context is created.

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Then it creates a global object, which is literally the same as a window object.

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You see that we have here a window object.

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If we drop down it, you will see here a list of multiple properties and methods which are already built

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in.

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So the window object represents an open window in the browser.

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In other words, when the original document is loaded, the browser creates a window object for it.

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If we write your key word this.

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Which is already created when the page was loaded, it will give us the exact same window object.

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So this is a special keyboard.

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It always refers to the object.

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And on a global level, it refers to global window object.

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The key word, this is frequently used in JavaScript and you will meet it a lot of times throughout

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the course.

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OK, so you see that all this stuff happens without any single line of code of JavaScript and even without

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linking JavaScript file to HTML document.

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All right, now let's get rid of these comments and make a link working, that is cryptologist file

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create variable name equals to John.

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Reload and now let's check a window object right window.

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Then drop down it scroll and you see that here we have our variable name and its value, John.

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So when the variable is created outside the function, it's on global level.

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And actually it is assigned to the global window object as a property.

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So if we write, name will get John.

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And who write it as a window name?

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Evalu will be the same.

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Also, the result will be the same if we use this key word.

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Because on a global level, this refers to global window object.

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All right, in the same way, we can create function on global level, so right here, function A.

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And then right return hello.

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Reload and type again or window.

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And you can see here that the function is attached to global window object as a method.

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In order to call this function, we need to write your function, name A with parentheses.

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So we got hello.

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And we can call this function as a method of global window object, for that, we need to write window

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dot.

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A.

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And you see that we have again, hello.

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OK, in order to make it clearer, let's create an object.

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With a property

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name and right here, Niek, then create the method.

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Might be function and then return hi.

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Reload the page, you know that if you want to access on the property or on the method of the object

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we have just created, it's mandatory to indicate at first the name of the object.

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So write object name.

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And then object.

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Dalts.

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B, which is the name of the method.

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But in case of the global level, JavaScript allows us to access on variables and functions without

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indicating a window object or QAD each time.

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All right, for summarizing this lecture, let's briefly recall what we have just learned.

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So when Actimel Page is loaded in a Web browser, then the global execution context is created, which

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then creates global object, which is a global window object and a special quixotes, which on global

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level refers to global window object.

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All right, I hope that everything was clear to know those details is very important and it will be

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very useful and helpful for you in the future.

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See you in the next video.