All language subtitles for 008 Understanding Type Aliases_en

Now the more TypeScript code you're going to

write, the higher the chances that

at some point you might be repeating some type definition.

And we're actually already doing this here.

Here, for people, I'm saying that I want an array

of this kind of object.

So that I want an array full

of objects that have this structure.

And that's the same object I have up here

for person.

The same type definition just in the non array form.

But the object type is the same.

Now you can, of course, duplicate the type definition

but it's more realistic that you wanna

avoid that duplication.

And for that, you can create a so-called type alias.

You can define your own base type

in which a more complex type definition is stored

and then use that type alias instead

of repeating the entire type definitions.

For that here, for example, before we use this object type

for the first time here, we can define such a type alias

with the type keyword.

And that's a keyword which does not

exist in standard JavaScript but

which is added by TypeScript instead.

Now, after this type keyword, you use any name

of your choice which will be your new type name.

For example, person, like this.

And then after the equal sign here

you then have a type definition

because this is a pure TypeScript feature.

This will basically be thrown out

of the window when the code is compiled to JavaScript.

So, here on the right side of the equal sign

it's not a JavaScript value, but instead a type definition.

And that could be our object type definition here

which I now store here in this person type.

And now in all those places where I used this object type

I can use my alias instead now.

And it's therefore still the same type

but I only define it once.

And then I can repeat it in all the places where I need it.

And I can still also change it like I'm doing it

down here to use it just as person like this,

or to use it as an array full of persons.

That also works.

And that's the very important feature of type aliases

which can save you a lot of typing work

and which can, therefore, make your code more concise

and easier to maintain.