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Now that we've gotten through some administrative stuff, we're now going to dive into our first technical

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topic and start to discuss exactly what typescript is.

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So what is TypeScript, you know, what are we doing here?

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Well, at the end of the day, I want you to imagine that when we write typescript code, we are really

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just writing JavaScript.

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That's what's really happening here.

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We're still writing JavaScript.

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All the knowledge you have around JavaScript like arrays, objects, functions and even E 2015 syntax

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like restructuring and error functions and classes.

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All that knowledge still applies to the world of TypeScript as well.

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The only thing that we're really doing with TypeScript is adding in a little bit additional syntax to

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our code to handle something called the type system.

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This is what TypeScript is all about, as you might guess, and it's what we're going to spend the vast

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majority of this course learning about.

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So let's get a quick overview on the type system and understand what's going on with it.

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The goal of the type system is to help us catch errors during development.

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In other words, when we're actually writing our code in our code editor, think about how we catch

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errors right now with JavaScript code.

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Let's imagine that you're writing out some amount of JavaScript inside of your editor and maybe there's

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a bug inside of it.

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How would you find that bug?

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Well, really, with JavaScript, the only way to do that is to actually execute your code and see that

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air up here, and that's not super efficient.

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So as an improvement to the development workflow, we use the type system to help us catch errors during

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development while you and I are writing our code, typescript is going to be constantly analyzing it

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and looking for bugs.

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If it finds any possible bug, it's then going to pop open an error message inside of your code editor

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and tell you, hey, something might be wrong here.

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And that's going to essentially be a signal to you as a developer that you might need to fix up your

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code.

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Not to do this, er checking the typescript compiler is going to use something called type annotations

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to analyze our code base, you and I are going to be responsible for adding in these type annotations.

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You can kind of think of these type annotations as being like little comments to describe the purpose

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of our code or the information that is flowing through our program.

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The type system is only active during development, so in other words, once we go to deploy our application

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or even run it inside of our browser in a development environment, the entire type system falls away.

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Your browser has no idea what typescript is.

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And Narges likewise, no, JSC has no idea what typescript is either.

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So all this extra syntax are going to add into our code.

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Never makes it into the browser.

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It never makes it into Noguez.

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We're going to first compile our typescript and we're going to get some JavaScript out of that.

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And that JavaScript is what we're going to actually execute.

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Finally, this is something I want to point out, just because it's a little bit different than other

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languages that are strongly typed, the typescript compiler does not do any performance optimization

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whatsoever.

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Now, this is very different than many other languages.

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In many other languages, the type system can be used to optimize some code that you write using the

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compiler.

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But that is not the case here with TypeScript.

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All right, so that kind of help you understand this process here, let's run through the common scenario

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of how we're going to actually write some code and run it inside the browser or with Narges.

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So you and I are going to write some type code inside of our editor and remember, we can think of TypeScript

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as really just being plain JavaScript, but with these type annotation things added in.

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Then once we want to actually run our code, we're going to feed that code into the typescript compiler.

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This is a command line tool that's going to read our code, check it for any possible errors, and then

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convert it into plain JavaScript.

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You and I are then going to take that JavaScript code and feed it into the browser or into Noguez and

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finally execute it.

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So, again, we do not execute, typescript, we always are executing JavaScript, and so when I say

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that you and I are still writing technically JavaScript code here, it is, because the code we're writing,

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it is going to end up as JavaScript.

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Just it has these extra little type annotation things in it.

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All right, so to give you a really practical example of this, I want to show you a quick little Web

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page here.

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This is a in browser type script compiler.

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It's going to open up this link inside of a new browser tab.

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Now, on the left hand side, you're going to see a little bit of typescript code, and I know this

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is kind of cut off right there, but I just want to give you the impression that this tight script right

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here has a bunch of additional syntax in it.

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Right.

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Just take a look at this code.

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We don't need to understand what it does.

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You can tell at just a glance that there's a lot of extra stuff in here and it does not look like normal

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JavaScript.

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So on the left hand side, we've got the typescript, this page is going to compile that code and then

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print out the equivalent JavaScript on the right hand side.

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So this is the output from the typescript compiler.

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And looking at that, yep, it sure looks like plain JavaScript.

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So I can't say it enough, like I said, I'm going to repeat it many times throughout this course,

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we're still writing JavaScript code.

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We're just adding in little extra pieces of syntax here and there.

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And these extra pieces of syntax are meant to help the typescript compiler understand what we're trying

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to do with our code base so it can help us catch errors.

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That's it.

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That's the entire typescript world.

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All right, let's do a quick wrap up on what we learned in this video.

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So first off, when we write TypeScript, we're still writing JavaScript.

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We're just adding in these extra little type annotation things.

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Secondly, typescript has no effect on how our code actually gets executed, in other words, there

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is no performance optimization or anything like that.

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Now, finally, the best way to think of TypeScript, in my opinion or kind of an effective analogy,

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is to think of TypeScript as being like a friend who is sitting behind you while you are writing code.

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And maybe that friend is looking at every line of code you're writing and helping you catch errors.

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That's what TypeScript is really doing for us.

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It is a helper to help us catch errors.

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It doesn't actually have any impact on the final code that we output or the actual code that we run

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inside the browser.

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It's just there during development.

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OK, so now we've got a better idea of TypeScript.

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Let's take a quick pause right here and we're going to do a little bit of environment set up in the

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next video.