1
00:00:02,390 --> 00:00:06,250
We're almost done with the basics about TypeScript and the core types.

2
00:00:06,290 --> 00:00:13,270
There are two more types which are good to be aware of because they will matter from time to time.

3
00:00:13,310 --> 00:00:21,170
The first type is the UN known type for Dad all named does fall here functions T S and add a new apt

4
00:00:21,200 --> 00:00:32,230
yes file and in their let's say we have a new variable user input and this is of type and known.

5
00:00:32,450 --> 00:00:38,330
It's not type any which would be the default but unknown which is a different type introduced by typescript.

6
00:00:38,580 --> 00:00:43,800
It might be unknown because we don't know yet what the user will eventually enter if it's a number if

7
00:00:43,800 --> 00:00:44,820
it's a string.

8
00:00:44,820 --> 00:00:46,800
We don't know.

9
00:00:46,830 --> 00:00:51,840
Now the interesting thing about the unknown type is we can store any value in there without getting

10
00:00:51,900 --> 00:00:53,280
errors.

11
00:00:53,280 --> 00:00:54,650
So this is all allowed.

12
00:00:54,660 --> 00:01:02,340
If I now compile my file here you see I get no compilation error so thus far it's the same as if we

13
00:01:02,340 --> 00:01:05,310
wouldn't have assigned a type here and hence we have any type.

14
00:01:05,310 --> 00:01:13,530
Or if he would have explicitly set any as a type but still unknown is different to any this year works

15
00:01:14,160 --> 00:01:21,060
but will run into issues if I have another variable let's say user name which should be a string and

16
00:01:21,060 --> 00:01:27,230
that's on initialized here but then here I want to set a user name equal to user input.

17
00:01:27,240 --> 00:01:32,890
Now you see we're getting an error that type unknown is not a sign to type string.

18
00:01:33,060 --> 00:01:38,120
So user name once a string and of course unknown is not guaranteed to be a string.

19
00:01:38,130 --> 00:01:41,630
Here I assigned one but that's just a case in this line.

20
00:01:41,670 --> 00:01:46,530
User input technically could hold any value because it's I'm known.

21
00:01:46,530 --> 00:01:52,440
Now the interesting thing is if I switch unknown to any this error goes away because any is the most

22
00:01:52,440 --> 00:01:58,500
flexible type and TypeScript and it basically disables all type checking and typescript just says I

23
00:01:58,500 --> 00:01:59,190
give up.

24
00:01:59,220 --> 00:02:06,780
Do whatever you want unknown is a bit more restrictive than any with unknown.

25
00:02:06,780 --> 00:02:13,530
We have to first of all check the type that's currently stored in user input before we can assign it

26
00:02:13,560 --> 00:02:16,230
to for example a variable that wants a string.

27
00:02:16,230 --> 00:02:24,370
So since a string is wanted here we could check if type of user input is equal to string and typescript

28
00:02:24,390 --> 00:02:30,780
will detect this check and understand that in here what is stored in user name because it's inside of

29
00:02:30,780 --> 00:02:36,540
this if statement where I check for a user input being of type String user input is guaranteed to be

30
00:02:36,540 --> 00:02:43,800
a string and Dale for I can safely assign to user name so I need such a extra type check here with unknown

31
00:02:44,040 --> 00:02:52,950
to be able to assign a unknown value to a value with a fixed type and Dale for unknown is the better

32
00:02:52,950 --> 00:03:00,600
choice over any if you know I can't tell exactly what type all stored in there it might be a number

33
00:03:00,600 --> 00:03:07,590
it might be a string but I know what I want to do with it eventually we'll just add an extra check to

34
00:03:07,590 --> 00:03:12,720
make sure that what you want to do can be done so that if you want to work with the string you have

35
00:03:12,720 --> 00:03:19,650
a string and you're good and then unknown is better than any because it makes sure that you're not allowed

36
00:03:19,650 --> 00:03:23,370
to do everything but you have at least some type checking.

37
00:03:23,370 --> 00:03:28,800
Of course if you have a chance of knowing in advance that user input is always a string or always a

38
00:03:28,800 --> 00:03:35,190
string or a number well then you should use string or such a union type instead of unknown so unknown

39
00:03:35,190 --> 00:03:41,280
still is a type you shouldn't use all the time but it is better than any for the reasons described.