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Now that we've got a better understanding of what a type is, let's dive a little bit deeper into the

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subject and then discuss why we care about types at all.

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All right.

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So first off, a couple examples of some very basic types.

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So any time that we are working with a value that has a type of string, we would expect to see a value

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that look like these right here.

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So if I have a value that looks like high there, that is a string.

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If I see a value that looks like a string with no characters, that is also string and something that

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says today's Monday.

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Yep, that's a string as well.

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Likewise, if I've got some really small decimal number, that's a number, a negative number has a

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number and a really large number is a number as well.

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And the reason I break out no right here is that in some other languages, there are actually subtypes

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of numbers.

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So for example, in other languages, you might have a type to represent numbers that have a decimal

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or you might have another type to represent a number that is only an integer and therefore doesn't have

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a decimal.

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In JavaScript or me in typescript, we have nothing like that, a number is a number, regardless of

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whether it is positive or negative, has a decimal, doesn't have a decimal there.

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All numbers.

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If we have a value of true or false, we would say that its type is Boolean and then remember, we are

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not only restricted to these basic types right here, every value in typescript has a type.

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So, for example, if we made a new date object, the resulting object from that would have a type of

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date.

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And then if we had an object that had an ID, a completed flag, a title flag, we would say that that

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is an object that has type to do.

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And this one only applies if we were working in a code base that had to find this interface right here.

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Remember this interface to find a new type.

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OK, so now we've seen some examples of different types.

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Let's talk about how all these types kind of relate to each other.

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So in the world of TypeScript, we have two different categories of types, we have primitive types

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and object types.

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Primitive types are all the very basic types that you might get.

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So like no strings, boolean null, undefined and then Simbel and void are two others we'll talk about

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later on.

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The other category we have access to are something called object types, and these are essentially any

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types that you and I create or any other types that are built into the language itself.

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So, for example, all the different functions that you and I create are going to have their own type.

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And those are a object type, any class you and I create or he's going to have its own type.

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Same thing with arrays and objects as well.

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Now, why is there the divide here, like why are there two categories, one called primitive types

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and one called object types?

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Well, the true answer to this, we won't quite see until later on.

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But just as a quick preview, we say that there is a separate category called object types right here,

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essentially because you and I can write some code that will essentially trick TypeScript into believing

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that one value is a different type.

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I know that sounds really confusing right now, but essentially we can kind of sometimes trick the typescript

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compiler in a very good way.

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We can do that with object types only.

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We can not do that with primitive types.

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So that's why we have these two separate categories.

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Again, I know that's confusing to hear right now.

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I just want to understand why you will sometimes see these broken out into the two separate categories.

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OK, so now that we understand a little bit more about type's until the last big question here, why

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do we care about Type's at all?

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If I had to answer that, I would say that there are two big reasons.

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The first one is that types are used by the types of compiler to analyze our code for errors.

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So think about the definition that we just gave or types.

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We just said that types are an easy way to refer to the different properties and functions that a value

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has.

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Just keep that in mind for a second while you keep in mind I'm going to flip back over my code editor

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and take a look at the code that we just wrote a little bit ago.

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So inside of here, we defined a new type.

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We said that we had a new type inside of application called to do and a to do is only ever going to

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have the properties ID title and completed.

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Then down here on line 12, we said that the variable to do was going to referred to an object of type

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to do so, that means that the object that this variable refers to is only ever going to have these

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properties.

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The typescript compiler can use that information.

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So if we start to refer to some property on that, to do variable that doesn't exist, TypeScript is

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going to throw in aretz.

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TypeScript knows that this variable refers to an object that has these properties and nothing else.

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So if we try to reference some other property, there must be something wrong with our code in.

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TypeScript can discover that and tell us that in the form of an error.

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So that's why we generally care about types.

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The other big reason that we care about types.

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Back over here, one more is that allows it allows other engineers to understand what values are flowing

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around in our code base.

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If you've ever worked on a large JavaScript project before, you might have ran into the scenario where

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you open up some file and you see some function in there with some really unclear argument name like

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maybe a function with an argument name of like the letter A and nothing else.

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In that case, on a large project, it might be really hard for you to understand what that function

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is doing.

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If we instead tried to annotate the type of arguments being passed into a function by labeling the types,

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then that at least gives other engineers some idea of what type of data is flowing around inside of

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application.

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And ultimately, it will make it slightly easier for other engineers to understand what our code is

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doing.

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So that's why we care about types, let's now take a quick pause right here.

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When we come back, the next video, we're going to start to take a look at some more code snippets

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to understand what's really going on.

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So quick pause and I'll see you in just a minute.