1
00:00:01,190 --> 00:00:05,300
In this video we're going to take a look at another example of when we're going to add in a type annotation

2
00:00:05,300 --> 00:00:06,200
manually.

3
00:00:06,230 --> 00:00:11,090
So this is going to be whenever we declare a variable on one line and then initialize it later as a

4
00:00:11,090 --> 00:00:16,070
quick reminder type inference only works when we do variable declaration and initialization on the same

5
00:00:16,070 --> 00:00:16,340
line.

6
00:00:16,750 --> 00:00:21,740
And so obviously if we split this into two separate steps or two different lines of code then type inference

7
00:00:21,740 --> 00:00:23,940
doesn't work anymore all right.

8
00:00:23,940 --> 00:00:28,200
So going to flip back over to my editor I'm again at the very bottom of my variables file I'm going

9
00:00:28,200 --> 00:00:36,210
to set up a second example here going to say when we declare a variable on one line and initialize it

10
00:00:36,300 --> 00:00:38,080
later OK.

11
00:00:38,090 --> 00:00:43,640
So for this example I'm going to make an array of strings called Words like so and I'm going to give

12
00:00:43,640 --> 00:00:52,980
this the words read green and blue then right after that I'm going to declare a variable called Bound

13
00:00:53,010 --> 00:00:54,940
word like s.

14
00:00:55,110 --> 00:00:56,370
So here's what I want to do.

15
00:00:56,370 --> 00:01:00,810
I want to write a for loop that's going to iterate through this array right here.

16
00:01:00,810 --> 00:01:09,060
And if I ever find a word or a string equal to green then I want to set found word to a true so if finds

17
00:01:09,300 --> 00:01:11,850
green inside of words just set found where to true.

18
00:01:11,850 --> 00:01:13,090
That's pretty much it.

19
00:01:13,110 --> 00:01:17,670
I know this is a silly example but I just want to give you a very practical example of when we're going

20
00:01:17,670 --> 00:01:24,500
to run into this type annotation stuff so I got to write out my for loop and say let I equals zero I

21
00:01:24,510 --> 00:01:34,180
less than words at length I plus plus and then for every word will say if words at i is equal to green

22
00:01:35,070 --> 00:01:43,830
then we'll set found word equal to true like so now in this case I have an instance where I'm declaring

23
00:01:43,830 --> 00:01:50,310
the variable up here and then I only assign it a value or initialize it down here inside of my for for

24
00:01:50,310 --> 00:01:55,640
loop if I know mouse over found word it will very clearly tell me that this is of type any and in fact

25
00:01:55,640 --> 00:02:00,650
I even have a little underlined here that is a warning that tells me that found word has an implicit

26
00:02:00,740 --> 00:02:01,830
any type.

27
00:02:02,210 --> 00:02:07,710
And then the tip here says that I might get a better type if I actually use the variable.

28
00:02:07,790 --> 00:02:13,160
Now when it says inferred from usage that actually means that like I have to add in the annotation right

29
00:02:13,160 --> 00:02:16,210
here or optionally initialize it on the same line.

30
00:02:16,220 --> 00:02:20,460
So in this case to make this warning go away we have to add in a type annotation.

31
00:02:20,780 --> 00:02:22,040
So I can tell typescript.

32
00:02:22,190 --> 00:02:22,550
All right.

33
00:02:22,550 --> 00:02:26,640
There's gonna be a boolean and now we get around that issue.

34
00:02:26,940 --> 00:02:31,620
So whenever type inference doesn't work because we are doing declaration and initialization on separate

35
00:02:31,620 --> 00:02:34,020
lines we're going to add any type invitation.

36
00:02:34,020 --> 00:02:35,590
That's pretty much it.

37
00:02:35,700 --> 00:02:39,960
Now as a quick aside here obviously the best way to write out this code would have been to do something

38
00:02:39,960 --> 00:02:42,170
like this to initialize found word is false.

39
00:02:42,330 --> 00:02:44,820
And now typescript understands what's going on here.

40
00:02:44,850 --> 00:02:47,310
This is way better code than what we had before.

41
00:02:47,340 --> 00:02:51,870
But again I just wanted to give you a quick example of where we might have a declaration on one line

42
00:02:51,930 --> 00:02:54,090
and then initialization at some future point.

43
00:02:55,300 --> 00:02:55,520
All right.

44
00:02:55,540 --> 00:02:56,730
Let's take a quick pause right here.

45
00:02:56,740 --> 00:03:00,610
When we come back in the next video we're going to take a look at our final example of when we are going

46
00:03:00,610 --> 00:03:02,760
to prefer to use a type invitation.

47
00:03:02,860 --> 00:03:04,600
It's a quick pause and I'll see you in just a minute.