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In this video.

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Let's talk about console dot log, the name that we have been mentioning from the beginning of this

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course.

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At this point, until this point, you all know what console log is, but it's time to learn more about

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console log.

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So let's get rocking.

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Well, console log is a function.

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One key word here is what is a function?

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Even looking at a syntax, you see we have the square braces telling you is a function and it is used

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to print any text to the console ranging from simple text variables, objects and arrays.

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That's one key point about console.log.

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The next point about console.log is that JavaScript console were built inside browsers and it is like

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a command line interface that runs JavaScript on your JavaScript engine.

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But behind the console is what we call read ever print and loop.

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And in short, we call it repo.

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All right.

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Let's talk more about this report.

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All right.

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So let's say that we are trying to run a simple function inside the console.

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So in the first place, it reads your input.

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All right.

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And then it evaluates it as JavaScript code and then it prints the results.

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That's a work of the repo, right?

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You sometimes hear the term repo being used to refer to any sort of programming shell that allows you

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to enter code and see results immediately.

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For instance, Node.js, Python and Ruby also provide similar repo shell.

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All right, so let's get back to console.log and try something.

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Let's open our console and do some simple calculations and let's see how it works behind the scene.

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Let's try to type this.

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Let's say one plus two.

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When I hit enter, it will see that I have the result.

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Three.

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How this thing happened is because of what you call the repo built inside.

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And if you are an object developer, you also have repo inside Node.js, meaning we are running JavaScript

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on the server so the same syntax can be run inside Node.js or a Node.js environment.

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So back to Visual Studio code.

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Let's try to run a simple Node.js command, even though we haven't gone there yet, but for some demonstration

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purposes, let's try it out.

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But for this one before it works, unless we have not been installed.

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But for now, don't worry if you don't have not been installed.

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So I will go to terminal here and a new terminal and inside my terminal to be able to execute repo or

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command inside my terminal.

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I'm going to use node and now hit enter and can see that now I'm in the repo of node.js so the same

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code I type one plus two when I hit enter, you see I have three.

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This is what we call the repo and we have the same repo inside browser.

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That is our console log.

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But have a look.

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You see that when you run this code as soon as it print the answer we have next line at that mean going

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to loop through its looping but let's try to run a simple function and let's the difference here.

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Let's try to run this function.

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Remember, console.log is a function, right?

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So let's say this function will say say hi.

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Now have a look.

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When I hit enter, two things are going to happen when I hit Enter.

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First, we have the resort.

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Say hello.

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And on second line, we see what is called undefined.

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Let me explain why this happened.

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When executing a function in the console, for example, using the console log.

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This one as we did well, it produces two lines of output.

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One is the result and one is on define.

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The first line is a result that we expect and indeed this is what we are expecting.

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Okay.

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The second line reads what is called undefined.

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Why I got undefined here.

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This is because the first line is the output that we instructed JavaScript to print, and the second

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line is a result of evaluating our program.

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The second line here you are trying to evaluate our program and in short our function called console.log.

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So every JavaScript expression has a result, but some expressions such as the console.log function,

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they all return an empty result called undefined.

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So any expression that does not return an answer, the repo we give us as undefined.

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All right, so that is it.

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About the console, that log.