1 00:00:02,120 --> 00:00:03,970 Now in our TypeScript code, 2 00:00:03,970 --> 00:00:06,070 we have some repetition. 3 00:00:06,070 --> 00:00:08,550 Not horrible and definitely bearable, 4 00:00:08,550 --> 00:00:10,690 but we have some repetition and some code 5 00:00:10,690 --> 00:00:12,300 that could be hard to read. 6 00:00:12,300 --> 00:00:14,610 For example here we have repetition, 7 00:00:14,610 --> 00:00:18,230 we re-use the same union type in two places. 8 00:00:18,230 --> 00:00:20,440 Now, this is definitely okay, 9 00:00:20,440 --> 00:00:22,140 but you could optimize this 10 00:00:22,140 --> 00:00:24,910 or improve this with a type alias. 11 00:00:24,910 --> 00:00:28,150 TypeScript has a built in type operator, 12 00:00:28,150 --> 00:00:30,510 which does not exist in JavaScript, 13 00:00:30,510 --> 00:00:34,120 don't confuse it with type of, type is a different one. 14 00:00:34,120 --> 00:00:37,630 This allows you to set up your own type alias 15 00:00:37,630 --> 00:00:40,370 so you can give a different type a new name. 16 00:00:40,370 --> 00:00:42,280 And that is especially useful 17 00:00:42,280 --> 00:00:45,140 if you're working with union types for example. 18 00:00:45,140 --> 00:00:49,410 We can have our num or string type for example, 19 00:00:49,410 --> 00:00:52,040 the name is up to you, you could name it like this, 20 00:00:52,040 --> 00:00:55,490 and the value which we store in there is now a type. 21 00:00:55,490 --> 00:00:57,520 So for example this union type. 22 00:00:57,520 --> 00:01:01,700 And now we can use num or string in all the places 23 00:01:01,700 --> 00:01:04,380 where we previously set up the union type. 24 00:01:04,380 --> 00:01:09,280 And you can store anything, any type in such a type alias. 25 00:01:09,280 --> 00:01:13,780 Now if you compile this, if you compile this code, 26 00:01:13,780 --> 00:01:16,530 this will be gone, you don't see the type alias there 27 00:01:16,530 --> 00:01:19,060 because it's a pure TypeScript feature. 28 00:01:19,060 --> 00:01:21,670 But it can save you some repetition. 29 00:01:21,670 --> 00:01:24,020 You can also use the type alias 30 00:01:24,020 --> 00:01:26,910 to for example store your object type. 31 00:01:26,910 --> 00:01:31,060 My result, and again that name is up to you, 32 00:01:31,060 --> 00:01:33,690 could be this object type. 33 00:01:33,690 --> 00:01:36,290 So I can cut it from down there, 34 00:01:36,290 --> 00:01:38,793 and now use result down there. 35 00:01:39,890 --> 00:01:41,793 And now I'm referring to this object. 36 00:01:45,110 --> 00:01:47,980 So type aliases can be very useful. 37 00:01:47,980 --> 00:01:51,030 An alternative, at least when you're working with 38 00:01:51,030 --> 00:01:54,410 object types are interfaces. 39 00:01:54,410 --> 00:01:56,450 Interfaces also allow you 40 00:01:56,450 --> 00:01:59,530 to define the structure of an object. 41 00:01:59,530 --> 00:02:04,260 For example result object, to avoid a name clash. 42 00:02:04,260 --> 00:02:07,640 Here I could paste in that exact same structure 43 00:02:07,640 --> 00:02:10,490 as for my result type alias. 44 00:02:10,490 --> 00:02:13,140 And I can now use result object 45 00:02:13,140 --> 00:02:15,800 where I previously used result. 46 00:02:15,800 --> 00:02:17,910 Now why would you use an interface 47 00:02:17,910 --> 00:02:20,810 or a type alias, what's the difference? 48 00:02:20,810 --> 00:02:23,330 If you're just defining the structure of an object, 49 00:02:23,330 --> 00:02:25,060 you can use either of the two. 50 00:02:25,060 --> 00:02:27,180 Using interfaces is a bit more common 51 00:02:27,180 --> 00:02:28,830 but it's not a must to. 52 00:02:28,830 --> 00:02:33,470 Interfaces can however also be used to force classes 53 00:02:33,470 --> 00:02:36,690 to implement certain methods or functionalities, 54 00:02:36,690 --> 00:02:39,910 but that's beyond the scope of this basics refresher, 55 00:02:39,910 --> 00:02:41,120 you do learn about it 56 00:02:41,120 --> 00:02:44,000 in my understanding TypeScript course though. 57 00:02:44,000 --> 00:02:47,493 So for basic type aliasing, it doesn't matter. 58 00:02:48,410 --> 00:02:52,570 So, here we have a type alias, here we have the interface. 59 00:02:52,570 --> 00:02:54,780 A last important note is that 60 00:02:54,780 --> 00:02:58,970 if you would add your own class or constructor function, 61 00:02:58,970 --> 00:03:02,060 you could use the class name as a type as well, 62 00:03:02,060 --> 00:03:04,060 just as we're using date here. 63 00:03:04,060 --> 00:03:07,120 We can use date with new date 64 00:03:07,120 --> 00:03:10,990 to instantiate it and get the current date time stamp, 65 00:03:10,990 --> 00:03:13,690 but we can also use it just as a type. 66 00:03:13,690 --> 00:03:17,130 And that's true for any constructor function and class, 67 00:03:17,130 --> 00:03:20,123 no matter if it's a built in one, or your own one.