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Alright, so in this video we're
going to talk about types. So
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with typescript you have
several types. But we're going
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to first work with primitives.
So primitives are the most
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basic types, okay? We have
number, string and boolean in
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lowercase, that's very
important. And then
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where we're going to discover
other types, okay? So these are
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I would say the the everyday
types that we're going to use,
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okay? So all of these ones, so
the primitives and this part of
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the advanced types. So arrays,
objects, functions,
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enameration, null and undefined
and void. Obviously we're going
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to cover all these types. And
then we have more occasional
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types so unknown never any so
any is very special because
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that's one of the types that
you should almost never use is
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very famous for not being liked
by the typescript community
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because when you're writing any
it basically means "I don't want
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to use typescript" this can
have any types so it it's
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basically like not using typescript
but we're going to talk
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about that later and obviously
there are other types a lot
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more that are more advanced and
you can even create your own
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types but we're going to talk
about that later in the course.
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For now we're going to work
with the primitives. So you can
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go back in your project. Uh and
by the way if you want to be
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able to start your project very
simply what you can do is you
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can go in your package dot
json and you can create a
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start comment that is basically
going to do what we do when we
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start the project. So a TSC
then you're going to target the
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index. TS file and just write
--watch this way now you
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can just type NPM start and
it's going to start a project
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and so let's say this is closed
now if I click on go live at
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the bottom since now my
projects in source I have to
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click here to open it for now
and now I'm in the index. HTML
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file okay so now we can go into
our index. TS and I'm just
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going to transform this awesome
variable into a let so I can
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reassign it so to type a
variable you can do it like
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this I can just do colon
string like this and now my
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awesome variable is a string
it's a string so now I cannot
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do something like this okay
this is not going to work and
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you have to learn how to read
type script errors so it's
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going to say that the type a
number so the number one is not
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assignable to the type string
okay so you cannot put a number
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into a string so now you have a
validation , typescript is
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going to help you know when
you're doing something wrong so
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you cannot do that for example
you could declare a number so
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I'm going to call it for
example value and it's going to
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be a number like this and it's
going to be one okay and again  
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you cannot do something like
this it's not going to work so
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you can declare a number like
this and you can even declare
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for example is cool variable
boolean is going to be true
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like this so now on each of my
variable I have a type that is
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affected and I can do awesome dot
and I will have only the
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functions that are related to
string that you can run on a
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string so for example to
lowercase and now the cool
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thing is that you even have syntax
checking so for example if I
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misspell this I will have some
help and it's going to say that
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to local "lowerase" does not
exist on type string but maybe
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I meant local lowercase so it's
going to try to find the best
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match for what you wrote so
also this is going to work okay
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and you can even use the quick
fix and I'm going to  say "change
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spelling" and it's going to fix
it for me if I want okay so
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that's another cool feature of
so now example here in my
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paragraph if I try to inject
something else than a string I
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should have an error because if
you pass your mouse over inner
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text you're going to notice
that inner text is a string so
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if I try to for example put
value in it it's not going to
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work and again you will have an
error that says number is not
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assignable to type string okay
so it's important that you
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learn how to read type script
errors okay sometimes they are
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not really meaningful but most
of the time they are so it's
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important to understand what's
going on okay so that's how you
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declare a type for a variable
but now you have to know
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something what we have done is
not really useful so I'm going
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to fix that you don't really
have to explicitly tell the
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type here on a primitive I
could actually remove it like
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this and you're going to say
why what's the point so I don't
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need types on primitive ? No you
don't. Because Typescript is
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smart enough to detect what is
the type of the variable if a
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primitive was assigned so here
as you can see it understood
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that it's going to be a string
here it understood that it's
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going to be a number and here a
boolean so I still have my type
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safety okay I still cannot do
something like this: awesome
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equal true for example this is
not going to work so with
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primitives there is something
called type inference and it's
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basically the behavior of type
script trying to find logically
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what is going to be the type of
your variable okay so you don't
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really need to specify
especially here the type but
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you'll see that we will have to
do that sometimes and mostly when we
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will create our own types
alright But for now, we're
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good. You don't need to do
that. So this is actually
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pretty much it about
primitives, okay? You don't
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really have to do anything,
they're just typed by default.
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Thanks to the type inference of
typescript. Alright, so see
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you in the next one to
continue.