1
00:00:00,180 --> 00:00:01,440
- Now in this video,
we're gonna be talking

2
00:00:01,440 --> 00:00:03,559
about a special type called the void type.

3
00:00:03,559 --> 00:00:04,770
And it's gonna be a rather short video.

4
00:00:04,770 --> 00:00:06,180
For example, if we hover over the sum,

5
00:00:06,180 --> 00:00:08,010
you know that the return
type of this sum function

6
00:00:08,010 --> 00:00:10,620
is a number and that's because
TypeScript infers that.

7
00:00:10,620 --> 00:00:12,420
Or we can manually come in here and say

8
00:00:12,420 --> 00:00:15,030
that the return type is going
to be number if we want.

9
00:00:15,030 --> 00:00:16,140
But what happens if a function

10
00:00:16,140 --> 00:00:18,060
doesn't actually return anything?

11
00:00:18,060 --> 00:00:19,410
Let's create a brand new function.

12
00:00:19,410 --> 00:00:20,790
This one's just gonna be print name.

13
00:00:20,790 --> 00:00:23,400
We're gonna pass it along
a name which is a string

14
00:00:23,400 --> 00:00:26,490
and it's just gonna
console.log that name variable.

15
00:00:26,490 --> 00:00:28,740
This function has no return at all.

16
00:00:28,740 --> 00:00:30,720
So what is the return type?

17
00:00:30,720 --> 00:00:31,980
Well, if we hover over print name,

18
00:00:31,980 --> 00:00:34,410
you can see the return
type is set to void.

19
00:00:34,410 --> 00:00:35,700
We could also manually say

20
00:00:35,700 --> 00:00:38,250
that this is going to be
a void return, as well.

21
00:00:38,250 --> 00:00:40,020
And all that means is that your function

22
00:00:40,020 --> 00:00:43,620
has no return keyword and
it doesn't return anything.

23
00:00:43,620 --> 00:00:45,390
This is a slightly different keyword

24
00:00:45,390 --> 00:00:48,390
than undefined, because
in JavaScript, by default,

25
00:00:48,390 --> 00:00:51,720
if you run a function and it
doesn't return anything at all

26
00:00:51,720 --> 00:00:54,720
it'll output undefined if you
try to set a variable to it.

27
00:00:54,720 --> 00:00:58,350
So if I just say const
a equals print name,

28
00:00:58,350 --> 00:01:00,120
pass it in a name,

29
00:01:00,120 --> 00:01:02,880
this a variable is technically undefined

30
00:01:02,880 --> 00:01:04,590
by JavaScript standards.

31
00:01:04,590 --> 00:01:06,780
But in TypeScript, we
actually differentiate

32
00:01:06,780 --> 00:01:09,270
undefined from void functions

33
00:01:09,270 --> 00:01:11,790
'cause they have a slightly
different meaning to them.

34
00:01:11,790 --> 00:01:14,100
When I say that a
function returns nothing,

35
00:01:14,100 --> 00:01:16,800
and by that I mean the
return type is set to void,

36
00:01:16,800 --> 00:01:19,200
I'm essentially saying that
there is nothing you can do

37
00:01:19,200 --> 00:01:20,430
with the return from this function.

38
00:01:20,430 --> 00:01:22,620
It doesn't return anything
and nothing that comes

39
00:01:22,620 --> 00:01:24,960
from it is useful in any way at all.

40
00:01:24,960 --> 00:01:26,250
While if I explicitly say

41
00:01:26,250 --> 00:01:28,320
that the function returns undefined,

42
00:01:28,320 --> 00:01:30,180
I can at least use that
in my TypeScript code

43
00:01:30,180 --> 00:01:32,610
because I know that this
thing is now undefined

44
00:01:32,610 --> 00:01:33,750
that it is returning from it.

45
00:01:33,750 --> 00:01:36,060
It's like an explicit
return type of undefined,

46
00:01:36,060 --> 00:01:37,800
while void is just explicitly saying

47
00:01:37,800 --> 00:01:39,120
this returns nothing at all

48
00:01:39,120 --> 00:01:41,310
and it never will return anything at all.

49
00:01:41,310 --> 00:01:43,470
So there's a slight
difference between those two.

50
00:01:43,470 --> 00:01:44,700
For example, if I were
to just come in here

51
00:01:44,700 --> 00:01:46,740
and I place a return
statement, now when I look

52
00:01:46,740 --> 00:01:48,960
at my print name, you can
see it's still a void type.

53
00:01:48,960 --> 00:01:51,630
'cause again, I'm returning
nothing all from my function.

54
00:01:51,630 --> 00:01:54,360
If I instead explicitly return undefined,

55
00:01:54,360 --> 00:01:55,800
you can now see the return type

56
00:01:55,800 --> 00:01:59,340
of this function has changed
to undefined from void.

57
00:01:59,340 --> 00:02:00,750
So if you want to return undefined

58
00:02:00,750 --> 00:02:03,480
from a function and use it
as undefined in TypeScript,

59
00:02:03,480 --> 00:02:05,700
you need to manually return undefined.

60
00:02:05,700 --> 00:02:08,820
But in 99% of cases, void
is going to work just fine

61
00:02:08,820 --> 00:02:09,780
'cause if you have a function

62
00:02:09,780 --> 00:02:12,270
that you don't want to return
anything from, or you are

63
00:02:12,270 --> 00:02:15,150
returning early by just
having the return statement,

64
00:02:15,150 --> 00:02:17,100
it makes sense that
this will be a void type

65
00:02:17,100 --> 00:02:19,823
'cause essentially it's saying
there's nothing there at all.