WEBVTT 1 00:00:01.440 --> 00:00:04.520 Welcome to Coding Challenge number three. 2 00:00:04.520 --> 00:00:07.293 And this is gonna be a quick and easy one. 3 00:00:09.260 --> 00:00:12.130 So all I want you to do is to rewrite 4 00:00:12.130 --> 00:00:14.906 the 'calcAverageHumanAge' function 5 00:00:14.906 --> 00:00:17.870 that we wrote in the previous challenge. 6 00:00:17.870 --> 00:00:20.500 Now the difference here is that this time, 7 00:00:20.500 --> 00:00:22.530 you should use an arrow function 8 00:00:22.530 --> 00:00:25.140 and you should use chaining. 9 00:00:25.140 --> 00:00:27.170 Now to make this chaining work, 10 00:00:27.170 --> 00:00:29.700 just keep in mind the second way that I used 11 00:00:29.700 --> 00:00:32.970 in the last challenge to calculate the average. 12 00:00:32.970 --> 00:00:35.710 Then, as always, use this test data here 13 00:00:35.710 --> 00:00:38.090 to try out your function. 14 00:00:38.090 --> 00:00:40.010 And so I'll see you here in a minute, 15 00:00:40.010 --> 00:00:42.793 line:15% or five minutes maybe, once you're done. 16 00:00:46.030 --> 00:00:48.890 Now all right, so let's grab the code here 17 00:00:48.890 --> 00:00:50.313 from the previous one. 18 00:00:51.960 --> 00:00:54.953 So there's no need to just rewrite everything. 19 00:00:58.320 --> 00:01:00.800 So let's get rid of all the comments here, 20 00:01:00.800 --> 00:01:02.273 all the console.logs. 21 00:01:03.910 --> 00:01:05.970 And so let's save it here, 22 00:01:05.970 --> 00:01:08.623 and then rewrite it as an arrow function. 23 00:01:13.000 --> 00:01:14.963 So it still takes in the ages, 24 00:01:16.370 --> 00:01:20.240 and now what it returns is simply the ages, 25 00:01:20.240 --> 00:01:22.053 then dot, this map, 26 00:01:23.370 --> 00:01:25.703 so calculating the human ages. 27 00:01:26.790 --> 00:01:29.810 Okay, and then on the result of that, 28 00:01:29.810 --> 00:01:33.930 we filter for only the adult docs. 29 00:01:33.930 --> 00:01:36.253 So when the age is greater than 18. 30 00:01:37.130 --> 00:01:39.003 So this is what we have for now. 31 00:01:40.040 --> 00:01:41.753 Let's call this one here two. 32 00:01:43.550 --> 00:01:48.130 Okay. And so for now this is the two erase that we have 33 00:01:48.130 --> 00:01:49.940 one for each function call. 34 00:01:49.940 --> 00:01:53.740 But now let's then also calculate the average. 35 00:01:53.740 --> 00:01:56.770 And so for that all we need to do is to chain 36 00:01:56.770 --> 00:01:59.580 this method of calculating the average. 37 00:01:59.580 --> 00:02:01.740 That he showed you in the last lecture, 38 00:02:01.740 --> 00:02:03.440 or actually in the last challenge. 39 00:02:04.780 --> 00:02:06.473 So pasting that here. 40 00:02:07.520 --> 00:02:11.300 And so now we get the exact same results as before, 41 00:02:11.300 --> 00:02:13.660 and that's actually already it. 42 00:02:13.660 --> 00:02:15.950 Now what's really important to notice here, 43 00:02:15.950 --> 00:02:19.820 is that this is actually really the only way 44 00:02:19.820 --> 00:02:22.300 of calculating the average now. 45 00:02:22.300 --> 00:02:25.180 So basically dividing the age by the length 46 00:02:25.180 --> 00:02:27.930 of the current array immediately here 47 00:02:27.930 --> 00:02:30.120 in each of the iteration. 48 00:02:30.120 --> 00:02:32.400 So remember that in the last challenge, 49 00:02:32.400 --> 00:02:35.380 I first simply added all the values together. 50 00:02:35.380 --> 00:02:39.580 And then afterwards I divided it by the length of the array. 51 00:02:39.580 --> 00:02:42.760 So in this case, by the length of the adults array. 52 00:02:42.760 --> 00:02:45.660 However, that would not work in this case. 53 00:02:45.660 --> 00:02:48.620 Because there would be no way of knowing the length 54 00:02:48.620 --> 00:02:50.300 of the adults array. 55 00:02:50.300 --> 00:02:53.100 So of this result here, right? 56 00:02:53.100 --> 00:02:55.180 Because we haven't stored it anyway. 57 00:02:55.180 --> 00:03:00.180 And so we couldn't do like this, like adults.length, right? 58 00:03:01.990 --> 00:03:03.340 This wouldn't be possible 59 00:03:03.340 --> 00:03:07.090 because adults here does not exist anywhere. 60 00:03:07.090 --> 00:03:09.930 And therefore we need to take that length 61 00:03:09.930 --> 00:03:12.120 from this input here. 62 00:03:12.120 --> 00:03:14.050 So from this fourth parameter, 63 00:03:14.050 --> 00:03:16.010 which gives us access to the array, 64 00:03:16.010 --> 00:03:18.770 on which the method is called. 65 00:03:18.770 --> 00:03:21.390 And that's the reason why I showed you this way here, 66 00:03:21.390 --> 00:03:22.870 in the last lecture. 67 00:03:22.870 --> 00:03:25.680 Because yeah, again this is the only way 68 00:03:25.680 --> 00:03:29.140 in which we can now calculate this average, 69 00:03:29.140 --> 00:03:31.470 unless we wanted to do it in two steps. 70 00:03:31.470 --> 00:03:32.770 But my instruction here 71 00:03:32.770 --> 00:03:35.930 was to really do it all with chaining. 72 00:03:35.930 --> 00:03:37.913 And so this is the way to go then. 73 00:03:39.330 --> 00:03:41.590 All right, so make sure you understand 74 00:03:41.590 --> 00:03:45.000 really why and also how this one here works. 75 00:03:45.000 --> 00:03:48.186 And then let's already move on to our next method, 76 00:03:48.186 --> 00:03:51.020 which is gonna be defined method. 77 00:03:51.020 --> 00:03:52.780 So another really cool one. 78 00:03:52.780 --> 00:03:54.623 So I can't wait to see you there.