1
00:00:00,730 --> 00:00:04,690
In this video we're going to get a better idea of what this angle bracket syntax is really doing for

2
00:00:04,690 --> 00:00:05,250
us.

3
00:00:05,350 --> 00:00:09,190
If you are already familiar with TypeScript and understand what generics are you can skip over this

4
00:00:09,190 --> 00:00:10,010
video entirely.

5
00:00:10,030 --> 00:00:16,180
Otherwise stick around the angle bracket syntax we see right here is the generic syntax inside a typescript.

6
00:00:16,360 --> 00:00:22,010
You can really think of these generic things as essentially being functions or types.

7
00:00:22,030 --> 00:00:25,720
Let me give you an example right now when we call model.

8
00:00:25,930 --> 00:00:30,850
We've got a function invocation right here or the set of parentheses when we normally call a function

9
00:00:30,880 --> 00:00:32,500
inside of typescript or JavaScript.

10
00:00:32,500 --> 00:00:38,470
We pass in a set of arguments those arguments customize how that function behaves the same thing is

11
00:00:38,470 --> 00:00:42,760
true or this list of generic type arguments as well.

12
00:00:42,760 --> 00:00:48,280
You can really think of these as being some arguments to the function of model but instead of being

13
00:00:48,340 --> 00:00:54,370
a data type or an actual value like let's say a string of user or this user schema thing it is instead

14
00:00:54,430 --> 00:00:55,390
a type.

15
00:00:55,390 --> 00:01:01,110
So again you can think of these as being types being provided to a function as arguments to really get

16
00:01:01,110 --> 00:01:02,990
a better idea of what's going on behind the scenes.

17
00:01:03,030 --> 00:01:08,590
I'm going to hold down command on my keyboard and then click on model if you're on windows you probably

18
00:01:08,590 --> 00:01:14,260
want to hit control and then click instead that will take us to the definition of what the model function

19
00:01:14,260 --> 00:01:15,370
is.

20
00:01:15,400 --> 00:01:21,840
This is the typescript definition of that function not the actual javascript implementation so there

21
00:01:21,840 --> 00:01:28,310
is a function called model and we can optionally provide to generic types to it.

22
00:01:28,320 --> 00:01:31,290
So here is generic type number 1 and generic type.

23
00:01:31,290 --> 00:01:34,370
Number two I know the syntax in here is really crazy.

24
00:01:34,410 --> 00:01:38,490
All you really need to understand once again is that these re centrally arguments that we are providing

25
00:01:38,490 --> 00:01:43,000
to this function they are not arguments in the same sense as normal arguments to a function that are

26
00:01:43,000 --> 00:01:43,620
used to.

27
00:01:43,620 --> 00:01:50,840
Instead they are customizing types so if we go back over to where we hold model we provided two types.

28
00:01:50,840 --> 00:01:52,890
User dock end user model.

29
00:01:52,940 --> 00:02:01,910
So those are going to show up as argument won and argument to so argument one is referred to as t that

30
00:02:01,910 --> 00:02:08,770
named T right there is the same as though we had some kind of argument name such as name or schema.

31
00:02:08,870 --> 00:02:14,720
We also have a second type argument that's going to be called you we can take a look at the function

32
00:02:14,720 --> 00:02:20,090
definition and get a better understanding of how these different types are actually being used in particular.

33
00:02:20,090 --> 00:02:21,950
Let's take a look at you right here.

34
00:02:21,980 --> 00:02:27,770
You'll notice that that you type is being used down here at the very end remember that this syntax right

35
00:02:27,770 --> 00:02:32,850
here is referring to the type of value that the function of model is going to return.

36
00:02:32,870 --> 00:02:37,440
So this right here says that whenever we call model we're going to be returning type you.

37
00:02:37,580 --> 00:02:38,970
And what is type you.

38
00:02:39,020 --> 00:02:45,260
Well it's whatever we pass in as the second generic type argument to the model function in our case

39
00:02:45,350 --> 00:02:51,020
our second type argument is user model and that means that we are saying that the model function over

40
00:02:51,080 --> 00:02:54,350
all is going to return something of type.

41
00:02:54,350 --> 00:02:59,690
User model and so if I actually go back over to and hover over user right here it says that user is

42
00:02:59,690 --> 00:03:02,060
going to be uptime user model.

43
00:03:02,060 --> 00:03:07,730
If I change the second argument right here to anything else then the model function is going to return

44
00:03:07,790 --> 00:03:10,990
a value of type whatever I put in there.

45
00:03:11,000 --> 00:03:16,910
So for example if I type in any now typescript the typescript thinks that the model function is going

46
00:03:16,910 --> 00:03:19,790
to return a value of type any.

47
00:03:19,820 --> 00:03:26,530
And so if I go and take a look at what gets assigned to user now user is of type any as well okay.

48
00:03:26,580 --> 00:03:32,830
So going to revert that back over to user model so again this is referred to as generics in typescript.

49
00:03:32,830 --> 00:03:36,200
This is a very brief very brief summary of what they're all about.

50
00:03:36,210 --> 00:03:42,520
They essentially allow us to customize the types being used inside of a function a class or an interface.

51
00:03:42,520 --> 00:03:44,760
We don't only need to understand a lot more beyond that right now.

52
00:03:44,770 --> 00:03:49,570
I just want to give you a very quick understanding of what the stuff is being used for.

53
00:03:49,600 --> 00:03:49,850
OK.

54
00:03:49,900 --> 00:03:52,480
Let's take a quick pause here and continue in just a moment.