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Okay so in the video we're
going to talk about objects. So
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we're going to use them a lot
so that's still a core
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concept. Uh so I'm going to
show you how to type an object.
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So let's say we have a print
coordinates function. So
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coordinates can be made of a
latitude and longitude. So we
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could expect an object in this
function. So I'm going to call
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that coords and I'm going to
type it as an object. And I
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will say and I will explicitly
provide my type by saying that
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it's going to be called lat and
it's going to be for example a
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string and a longitude that is
going to be a string so that's
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how you can type an object on
the fly directly in your
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parameters okay you can define
your type like this and then
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for example I could just
console log my lat that would
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be coords.lat and lng and that
will work well so you'll see
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that later we will find a way
to define our type outside and
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reuse them because if I want to
reuse my coords somewhere I
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will have to.. I will have to type
them again okay in another
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function so for example I don't
know get distance between and I
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would have a coords one and a
coords two and let's say this
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function returns the distance
between coords one
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and coords two, well you would
have to do this again.
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And so as you can see that can
rapidly become a waste of time
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to repeat the types and
redefine them everywhere so I
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will later show you a way to
declare a type and reuse it
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anywhere now let's say I create
a user , so as you can see
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I've created an object user
with some values and when I
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pass my mouse over since I have
declared my object directly and
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sent my values the inference is
working and as you can see my
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type has already been found by
typescript so I can just do a
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user. and as you can see I have
last name that is a string and
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my name that is a string and
let's say I decide to create a
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function that is displayUser
like this that is going to
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receive a user that is an
object that contain for example
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a first name that is a string
and the last name that is a
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string like this so I'm going
to change it here last name so
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it will match and inside let's
say I just display I don't know
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the first name so user.
firstName and I'm going to do
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a toLowerCase for example
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And I'm going to do the same
but for the last name.
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user.lastName that to
lowerCase. So this is
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going to work fine, if I do
a display user and send my user
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here oh and I made a mistake
here this should be first name
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as you can see yes it's working
now I just want to show you
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that you can also make an
attribute optional so for
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example let's say I say that my
last name is optional I can do
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that but as you can see well
since this can be undefined as
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you can see now the type of
last name is string or
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undefined typescript doesn't
know but, it knows that it
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can be one of these okay, so you
cannot call toLocaleLowerCase
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because that would be dangerous
okay if for some reason my My
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user doesn't have a last name
this is going to crash so what
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it can do is you can just check
if the user.lastName is
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defined and just by doing that
typescript is going to
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understand that all right now
here in this piece of code in
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this section there is no chance
that last name is undefined as
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you can see the type changes
because now it's it has to be a
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string because it cannot be
undefined in this if statement
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so you can do it like this or
you can use a shorter syntax
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and just use the question mark
like this this is going to
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check in the exact same way if
the last name is defined or not
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if it's defined then yes you
will be able to call to local
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lowercase and if it's not then
nothing is going to happen and
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it's just going to return
undefined and that's it okay
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but this way it's not going to
crash it's not going to call
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the function if it's undefined.
Alright so that is pretty much
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it about objects obviously this
may still be a little bit
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blurry okay for you because we
haven't really used them in a
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real project but we're going to
do that later, don't worry.
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Alright, so that's pretty much
about objects. See you in the
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next one.