1
00:00:02,300 --> 00:00:08,180
Kind of related to what you just learned about access modifiers is another modifier and that's the read

2
00:00:08,180 --> 00:00:09,590
only modifier.

3
00:00:09,650 --> 00:00:14,070
Let's say we have certain fields which should not just be private or public.

4
00:00:14,270 --> 00:00:18,170
They also shouldn't change after their initialization.

5
00:00:18,170 --> 00:00:23,570
For example the I.D. should not change their offer to make it clear that it shouldn't change.

6
00:00:23,570 --> 00:00:27,920
You can add read only here as well and you could have added that up here as well.

7
00:00:27,920 --> 00:00:32,290
So here you would have all the written Private Read only know the read only keyword.

8
00:00:32,330 --> 00:00:35,720
Just like private and public is introduced by typescript.

9
00:00:35,780 --> 00:00:38,000
It does not exist in JavaScript.

10
00:00:38,000 --> 00:00:44,210
It makes sure that if you tried to write to this property thereafter you fail so you can only use it

11
00:00:44,210 --> 00:00:46,540
once during initialization but thereafter.

12
00:00:46,550 --> 00:00:52,490
Let's save for ad employee for whatever reason I tried to change ideas to D2.

13
00:00:52,490 --> 00:00:59,270
You see we get an error here that I can't assign to I.D. because it's read only so does add some extra

14
00:00:59,270 --> 00:01:04,640
safety to make it really clear that a certain property should only be initialized to once and shouldn't

15
00:01:04,640 --> 00:01:05,840
change their offer.

16
00:01:05,960 --> 00:01:11,690
A requirement you have quite often for certain properties in your objects so this can add extra type

17
00:01:11,690 --> 00:01:14,950
safety again and make your intentions very clear.

18
00:01:14,990 --> 00:01:18,410
Of course you can always say well I'm the one writing the code.

19
00:01:18,410 --> 00:01:20,540
I won't do anything I don't want.

20
00:01:20,540 --> 00:01:27,380
Well it's still good to be very clear when you define your code because A you might forget what you

21
00:01:27,380 --> 00:01:28,280
wanted to do.

22
00:01:28,370 --> 00:01:33,800
If you paused working on your code for a couple of weeks or whatever it is and B you might be working

23
00:01:33,800 --> 00:01:40,160
in a team or sharing your code with our people and it's generally a good idea to write clearer and explicit

24
00:01:40,160 --> 00:01:45,290
code that makes our intentions very clear and read only can help you there because it makes it very

25
00:01:45,290 --> 00:01:47,140
clear what your goal is.

26
00:01:47,270 --> 00:01:53,420
If we have a look at app yes as I mentioned we see neither private nor public nor read only because

27
00:01:53,420 --> 00:01:57,650
that all only exists in typescript not in JavaScript.

28
00:01:57,650 --> 00:02:01,300
We also see something different which is also interesting.

29
00:02:01,460 --> 00:02:06,530
The methods are added to the prototype of our constructor function.

30
00:02:06,530 --> 00:02:11,420
Now for this you need to know what prototypes are and introducing those in this course would be a little

31
00:02:11,420 --> 00:02:16,110
bit too much attached you find some resources where you can dive into prototypes.

32
00:02:16,130 --> 00:02:20,510
It's an important part of JavaScript especially of JavaScript.

33
00:02:20,510 --> 00:02:26,150
Before we had classes and it doesn't hurt to understand prototypes if you're a javascript developer

34
00:02:26,540 --> 00:02:33,080
still here I will not dive deeper into them because it's a pure Javascript topic not specific to typescript.

35
00:02:33,080 --> 00:02:39,140
Indeed in typescript we typically work less with prototypes because we can do more with classes and

36
00:02:39,140 --> 00:02:40,130
related to that.

37
00:02:40,130 --> 00:02:43,340
We got another important class concept inheritance.