WEBVTT 1 00:00:01.380 --> 00:00:04.530 So as we reach the end of this section, 2 00:00:04.530 --> 00:00:08.640 let's quickly review all the terminology around classes 3 00:00:08.640 --> 00:00:11.650 because there is so much different stuff going on. 4 00:00:11.650 --> 00:00:15.270 So a lot of different features that you can use. 5 00:00:15.270 --> 00:00:17.800 And since classes are probably the way 6 00:00:17.800 --> 00:00:21.230 you're gonna implement OOP by yourself, 7 00:00:21.230 --> 00:00:25.200 it's always good to have a nice overview of everything 8 00:00:25.200 --> 00:00:26.453 that we can do with them. 9 00:00:28.510 --> 00:00:30.950 So here we have a huge class, 10 00:00:30.950 --> 00:00:34.060 which essentially contains all the features 11 00:00:34.060 --> 00:00:37.740 that we studied over the last couple of lectures. 12 00:00:37.740 --> 00:00:41.370 So this is how we define a class. 13 00:00:41.370 --> 00:00:44.810 And in this case, it is actually a child class. 14 00:00:44.810 --> 00:00:49.810 So student is a child class of the parent class person 15 00:00:49.860 --> 00:00:53.550 and that is because here we are using the extends keyboard 16 00:00:53.550 --> 00:00:57.730 to set up the inheritance between these two classes. 17 00:00:57.730 --> 00:01:00.130 And remember that the extends keyword 18 00:01:00.130 --> 00:01:04.560 will also automatically set up the prototype chain for us. 19 00:01:04.560 --> 00:01:06.803 So we don't have to do anything manually. 20 00:01:07.670 --> 00:01:11.570 Next up, this is how we define a public field. 21 00:01:11.570 --> 00:01:14.920 So this is what we did in a very recent lecture. 22 00:01:14.920 --> 00:01:19.080 And so remember that a public field is very similar 23 00:01:19.080 --> 00:01:22.980 to just a property that we defined in a constructor. 24 00:01:22.980 --> 00:01:26.550 So it is available on every created object. 25 00:01:26.550 --> 00:01:29.793 So on every instance created by this class. 26 00:01:30.730 --> 00:01:33.750 Then of course, we also have private fields 27 00:01:33.750 --> 00:01:36.920 and they are almost the same as public fields, 28 00:01:36.920 --> 00:01:40.980 but they are not accessible outside of the class. 29 00:01:40.980 --> 00:01:42.920 And so therefore this is perfect 30 00:01:42.920 --> 00:01:47.080 for implementing data privacy and encapsulation. 31 00:01:47.080 --> 00:01:49.940 We also have static public fields. 32 00:01:49.940 --> 00:01:53.180 And so these are fields or like properties 33 00:01:53.180 --> 00:01:56.510 that are available only on the class. 34 00:01:56.510 --> 00:01:58.690 And I didn't show them to you in the code. 35 00:01:58.690 --> 00:02:00.830 So in one of the lectures, 36 00:02:00.830 --> 00:02:03.120 but this is how we can implement them. 37 00:02:03.120 --> 00:02:05.570 So just like static methods, 38 00:02:05.570 --> 00:02:10.223 we use the static keyword to make any field static as well. 39 00:02:11.160 --> 00:02:14.180 Then here, this is the constructor method 40 00:02:14.180 --> 00:02:17.400 and it is automatically called by the new operator 41 00:02:17.400 --> 00:02:20.790 whenever we create a new instance of the class. 42 00:02:20.790 --> 00:02:23.440 So basically a new object. 43 00:02:23.440 --> 00:02:26.380 And this constructor method is mandatory 44 00:02:26.380 --> 00:02:29.800 in any regular class, but it might be omitted 45 00:02:29.800 --> 00:02:33.870 in a child class if we want it to have the exact same number 46 00:02:33.870 --> 00:02:36.873 and the exact same name of parameters. 47 00:02:38.610 --> 00:02:42.390 Then inside of the constructor there is the call 48 00:02:42.390 --> 00:02:47.180 to the parent class and so that is the superclass. 49 00:02:47.180 --> 00:02:49.860 And this of course is only necessary 50 00:02:49.860 --> 00:02:52.920 whenever we are writing a child class. 51 00:02:52.920 --> 00:02:56.190 So when we're using the extent keyword. 52 00:02:56.190 --> 00:02:58.500 And remember that this one needs to happen 53 00:02:58.500 --> 00:03:02.023 before we access the disc keyword in the constructor. 54 00:03:03.790 --> 00:03:06.800 Then here we have an instance property. 55 00:03:06.800 --> 00:03:09.430 And so just like public fields, 56 00:03:09.430 --> 00:03:13.900 the property is also available on each created object. 57 00:03:13.900 --> 00:03:16.830 But the difference between this one and the public field 58 00:03:16.830 --> 00:03:19.610 is that we set these instance properties 59 00:03:19.610 --> 00:03:23.200 based on input data of the constructor. 60 00:03:23.200 --> 00:03:26.380 So basically these properties are more personalized 61 00:03:26.380 --> 00:03:30.410 and unique for each object while the fields are usually 62 00:03:30.410 --> 00:03:33.620 for something that is common to all the objects. 63 00:03:33.620 --> 00:03:37.230 For example, here at the university for all of the students 64 00:03:37.230 --> 00:03:39.540 is the University of Lisbon. 65 00:03:39.540 --> 00:03:43.653 And so that is not unique to each object, okay. 66 00:03:44.720 --> 00:03:48.750 Then here we are redefining a private field. 67 00:03:48.750 --> 00:03:51.790 And so this is what we did with the pin 68 00:03:51.790 --> 00:03:54.930 in the bank account example, right? 69 00:03:54.930 --> 00:03:59.780 So this private field should be unique for each student. 70 00:03:59.780 --> 00:04:02.760 And so we created the private fields out there 71 00:04:02.760 --> 00:04:04.180 without any value. 72 00:04:04.180 --> 00:04:07.760 And then here we are simply redefining it to the value 73 00:04:07.760 --> 00:04:09.833 that is coming into the constructor. 74 00:04:11.400 --> 00:04:15.313 Then here, as we already know, is a normal public method. 75 00:04:16.640 --> 00:04:19.680 Here, we are referencing a private field 76 00:04:19.680 --> 00:04:22.280 and also a private method. 77 00:04:22.280 --> 00:04:24.703 And so about the private methods, 78 00:04:24.703 --> 00:04:27.120 this is how they look like. 79 00:04:27.120 --> 00:04:28.440 But as I mentioned, 80 00:04:28.440 --> 00:04:31.800 they will probably not yet work in your browser. 81 00:04:31.800 --> 00:04:33.940 At least if you're watching this close 82 00:04:33.940 --> 00:04:36.520 to the recording date of this course. 83 00:04:36.520 --> 00:04:40.030 So as an alternative, you can fake private methods 84 00:04:40.030 --> 00:04:43.873 by using the underscore convention instead of the hash. 85 00:04:45.150 --> 00:04:49.270 Next up, this is what a getter method looks like. 86 00:04:49.270 --> 00:04:52.400 And remember that a getter method is basically 87 00:04:52.400 --> 00:04:55.540 so that we can get a value out of an object 88 00:04:55.540 --> 00:04:59.800 by simply writing a property instead of writing a method. 89 00:04:59.800 --> 00:05:02.860 So in this case, we could simply write student.testscore 90 00:05:04.094 --> 00:05:07.520 and that would then run this getter method 91 00:05:07.520 --> 00:05:10.480 and the same for the setter method. 92 00:05:10.480 --> 00:05:13.740 So in this case, we can simply define the test score 93 00:05:13.740 --> 00:05:15.910 by setting it to some value 94 00:05:15.910 --> 00:05:19.450 instead of calling a test score method. 95 00:05:19.450 --> 00:05:22.300 And keep in mind that if you have a setter 96 00:05:22.300 --> 00:05:26.500 for a property that is already defined in the constructor, 97 00:05:26.500 --> 00:05:29.830 then you need to create basically a new property 98 00:05:29.830 --> 00:05:32.530 with the underscore in front of it. 99 00:05:32.530 --> 00:05:35.570 So again, that is kind of a convention 100 00:05:35.570 --> 00:05:37.720 that you should use in this case. 101 00:05:37.720 --> 00:05:40.320 And then in the getter with the same name, 102 00:05:40.320 --> 00:05:44.190 you also need to then return that new property. 103 00:05:44.190 --> 00:05:46.580 So we did that in one of the lectures, 104 00:05:46.580 --> 00:05:49.690 when we did a name validation for the name 105 00:05:49.690 --> 00:05:52.270 that was passed into the constructor. 106 00:05:52.270 --> 00:05:53.103 Remember that? 107 00:05:54.940 --> 00:05:58.480 Next, this is how your write static methods 108 00:05:58.480 --> 00:06:02.700 and a static method is available only on the class. 109 00:06:02.700 --> 00:06:07.230 So it cannot access the instance properties nor the methods, 110 00:06:07.230 --> 00:06:08.873 but only the static ones. 111 00:06:09.710 --> 00:06:12.460 So for example, that static public fields 112 00:06:12.460 --> 00:06:14.530 that we defined there in the top 113 00:06:14.530 --> 00:06:18.190 will of course be accessible in the static method. 114 00:06:18.190 --> 00:06:20.950 And usually we use these static methods 115 00:06:20.950 --> 00:06:23.423 as helper methods for the class. 116 00:06:24.670 --> 00:06:28.450 Finally, this is how you then create a new object 117 00:06:28.450 --> 00:06:30.650 using the new operator. 118 00:06:30.650 --> 00:06:33.893 And so this should be nothing new at this point for you. 119 00:06:35.370 --> 00:06:37.580 Now, here's just a couple of things 120 00:06:37.580 --> 00:06:40.020 that we need to remember about classes 121 00:06:40.020 --> 00:06:43.550 and that I actually already mentioned before as well. 122 00:06:43.550 --> 00:06:46.750 So keep in mind that classes are really just 123 00:06:46.750 --> 00:06:50.250 syntactic sugar over constructor functions. 124 00:06:50.250 --> 00:06:55.250 Also classes are not hoisted, they are first class citizens 125 00:06:55.300 --> 00:06:59.930 and the class body is always executed in strict mode. 126 00:06:59.930 --> 00:07:02.870 Okay, and there you'll have it. 127 00:07:02.870 --> 00:07:06.110 This is an overview and also a summary 128 00:07:06.110 --> 00:07:09.593 of the entire syntax of classes in JavaScript.