All language subtitles for 006 Understanding Type Inference_en

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Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:02,050 --> 00:00:04,800 Now, that we have learned about those base types 2 00:00:04,800 --> 00:00:08,450 before I dive into functions and parameters, 3 00:00:08,450 --> 00:00:11,500 I wanna talk about type inference. 4 00:00:11,500 --> 00:00:14,360 In all those examples, which are listed here, 5 00:00:14,360 --> 00:00:18,450 I always declared a variable with a type assigned. 6 00:00:18,450 --> 00:00:22,600 And then in a second step, I set a value. 7 00:00:22,600 --> 00:00:26,320 Now, often in programming, you do that in one step. 8 00:00:26,320 --> 00:00:28,500 You create a variable 9 00:00:28,500 --> 00:00:31,983 and you then already immediately assign an initial value. 10 00:00:32,950 --> 00:00:36,480 So therefore here let's talk about type inference. 11 00:00:36,480 --> 00:00:38,960 And let me show you what that is. 12 00:00:38,960 --> 00:00:41,350 Let's say we have another variable down here. 13 00:00:41,350 --> 00:00:45,260 The course variable. And in that course variable, 14 00:00:45,260 --> 00:00:47,490 I wanna store the name of a course 15 00:00:47,490 --> 00:00:50,840 like react the complete guide. 16 00:00:50,840 --> 00:00:52,330 Like this. 17 00:00:52,330 --> 00:00:55,850 Now, if I create this variable like this, and thereafter 18 00:00:55,850 --> 00:00:59,972 I try to store a number for an example, the course ID 19 00:00:59,972 --> 00:01:03,130 then you will see that I get an error, 20 00:01:03,130 --> 00:01:06,573 because the type number is not assignable to type string. 21 00:01:07,500 --> 00:01:10,400 But why am I getting this error? 22 00:01:10,400 --> 00:01:13,970 After all, I don't define a type anywhere. 23 00:01:13,970 --> 00:01:17,910 Well, here TypeScript used its powerful feature 24 00:01:17,910 --> 00:01:20,200 of type inference. 25 00:01:20,200 --> 00:01:24,040 By default, TypeScript tries to infer 26 00:01:24,040 --> 00:01:26,230 as many types as possible. 27 00:01:26,230 --> 00:01:29,770 So it tries to know which types are used 28 00:01:29,770 --> 00:01:34,110 where, without you explicitly stating those types. 29 00:01:34,110 --> 00:01:36,763 Which means that you need to write less code. 30 00:01:37,620 --> 00:01:42,030 I could also set my type here as we learned it. 31 00:01:42,030 --> 00:01:45,570 That would not be wrong, but it's redundant 32 00:01:45,570 --> 00:01:49,070 because if you immediately initialize this variable 33 00:01:49,070 --> 00:01:53,400 with a type TypeScript, will look at the value type here. 34 00:01:53,400 --> 00:01:57,320 So it will see that we stored a string in that variable. 35 00:01:57,320 --> 00:02:00,190 And it will then use that value type 36 00:02:00,190 --> 00:02:03,970 as an inferred type for this variable. 37 00:02:03,970 --> 00:02:08,340 And if you then try to assign a different type thereafter 38 00:02:08,340 --> 00:02:12,510 you'll get an error, because of type inference. 39 00:02:12,510 --> 00:02:14,810 And it is considered a good practice 40 00:02:14,810 --> 00:02:19,310 and a good idea to embrace that type inference feature. 41 00:02:19,310 --> 00:02:23,250 So to not unnecessarily specify the type 42 00:02:23,250 --> 00:02:26,710 in addition, you can do that you can explicitly 43 00:02:26,710 --> 00:02:29,570 state to type, but it's really redundant. 44 00:02:29,570 --> 00:02:32,660 It just means more word from your side and therefore 45 00:02:32,660 --> 00:02:34,180 you should not do that. 46 00:02:34,180 --> 00:02:35,830 You should instead stick 47 00:02:35,830 --> 00:02:40,240 to that type inference and use it whenever possible. 48 00:02:40,240 --> 00:02:43,360 And that's another super important feature 49 00:02:43,360 --> 00:02:45,313 which I wanted to highlight here. 3962

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