WEBVTT 1 00:00:01.270 --> 00:00:03.430 Let's now return to our code 2 00:00:03.430 --> 00:00:07.253 and learn how logical operators work in JavaScript. 3 00:00:09.270 --> 00:00:11.690 And let's actually use the Boolean variables 4 00:00:11.690 --> 00:00:13.310 from the last lecture. 5 00:00:13.310 --> 00:00:16.520 So the one about having a drivers license 6 00:00:16.520 --> 00:00:18.053 and having good vision. 7 00:00:20.460 --> 00:00:24.460 So, we are gonna create a variable for each of them. 8 00:00:24.460 --> 00:00:28.957 And the first one will be has drivers license 9 00:00:30.450 --> 00:00:33.440 and let's start by setting it to true. 10 00:00:33.440 --> 00:00:35.970 And remember that this one was variable A. 11 00:00:37.576 --> 00:00:41.283 And then let's create has good vision 12 00:00:44.190 --> 00:00:46.813 and also, let's initialize it with true. 13 00:00:48.250 --> 00:00:51.290 So these were the two A and B variables 14 00:00:51.290 --> 00:00:54.450 that we used in the last lecture as an example. 15 00:00:54.450 --> 00:00:57.263 And so it's a good idea to use these here as well. 16 00:00:58.650 --> 00:01:00.981 Okay, but now let's get started with the end 17 00:01:00.981 --> 00:01:03.530 and or operators. 18 00:01:03.530 --> 00:01:07.910 So let's log to the console, of using the end operator 19 00:01:07.910 --> 00:01:09.910 on these two variables. 20 00:01:09.910 --> 00:01:12.460 So has drivers license 21 00:01:12.460 --> 00:01:16.990 and now the end operator in JavaScript is this one. 22 00:01:16.990 --> 00:01:20.160 So it is we can combine two logical values. 23 00:01:20.160 --> 00:01:25.160 So has drivers license and has good vision. 24 00:01:26.570 --> 00:01:29.490 So let's see what the result will be. 25 00:01:29.490 --> 00:01:32.160 So this one is true, right? 26 00:01:32.160 --> 00:01:34.220 And this one is true as well. 27 00:01:34.220 --> 00:01:39.220 So the result of true and true, should be true, right? 28 00:01:41.200 --> 00:01:46.200 So let's see and yes, so that works. 29 00:01:47.010 --> 00:01:50.223 But now, of course, we will change one of them to false. 30 00:01:51.410 --> 00:01:56.410 So remember, the result of true and false will be false, 31 00:01:56.810 --> 00:01:59.870 because it's enough for one variable to be false 32 00:01:59.870 --> 00:02:03.100 for the result of the operation to be false. 33 00:02:03.100 --> 00:02:05.360 And so here, we can now confirm that 34 00:02:05.360 --> 00:02:07.990 and indeed, that is the result. 35 00:02:07.990 --> 00:02:10.450 But now let's see what it would look like 36 00:02:10.450 --> 00:02:12.670 with the OR operator. 37 00:02:12.670 --> 00:02:16.053 So I just copy this and paste it here. 38 00:02:17.070 --> 00:02:21.900 Now, instead of end we use OR and that looks like this. 39 00:02:21.900 --> 00:02:25.970 So again, true or false. 40 00:02:25.970 --> 00:02:27.620 What do you think it will be? 41 00:02:27.620 --> 00:02:32.400 Remember from the last lecture and the result is true. 42 00:02:32.400 --> 00:02:35.750 So it's enough for one of the variables to be true 43 00:02:35.750 --> 00:02:38.660 for the whole operation to become true. 44 00:02:38.660 --> 00:02:42.250 So I hope that's nothing new at this point. 45 00:02:42.250 --> 00:02:47.250 And of course, finally we can also use the NOT operator 46 00:02:47.490 --> 00:02:50.410 to basically invert one of the values. 47 00:02:50.410 --> 00:02:55.090 And the NOT operator in JavaScript is the exclamation mark. 48 00:02:55.090 --> 00:02:59.293 So not has driver's license will become, 49 00:03:00.670 --> 00:03:04.153 so it will change from true to false. 50 00:03:05.210 --> 00:03:09.280 All right, and now since we know how all of this works, 51 00:03:09.280 --> 00:03:12.490 we can use these variables to take a decision. 52 00:03:12.490 --> 00:03:14.660 So let's say that we want to determine 53 00:03:14.660 --> 00:03:17.370 whether Sarah should drive or not. 54 00:03:17.370 --> 00:03:20.960 So let's create a new Boolean variable and use the others 55 00:03:20.960 --> 00:03:22.183 to determine that. 56 00:03:24.620 --> 00:03:29.390 So let's say should drive 57 00:03:29.390 --> 00:03:32.070 and our model is that Sarah should drive, 58 00:03:32.070 --> 00:03:34.180 if she has a driver's license 59 00:03:34.180 --> 00:03:38.040 and at the same time has good vision, okay? 60 00:03:38.040 --> 00:03:40.570 And so as I mentioned in the last lecture, 61 00:03:40.570 --> 00:03:42.880 we can now use these Boolean variables, 62 00:03:42.880 --> 00:03:46.670 and this Boolean logic to model complex situations. 63 00:03:46.670 --> 00:03:49.140 And this one is actually pretty simple, 64 00:03:49.140 --> 00:03:52.750 but we will take it up a notch by the end of this lecture. 65 00:03:52.750 --> 00:03:57.430 So remember, model is that she has a driver's license, 66 00:03:57.430 --> 00:04:00.483 and that she has good vision. 67 00:04:01.540 --> 00:04:04.700 Okay, and now we can use this variable 68 00:04:04.700 --> 00:04:06.903 to finally take the decision. 69 00:04:08.010 --> 00:04:12.470 So let's then use this Boolean variable here and say, 70 00:04:12.470 --> 00:04:17.470 if she should drive, then lock to the console. 71 00:04:19.300 --> 00:04:22.750 Sarah is able to drive 72 00:04:24.130 --> 00:04:25.023 and if not, 73 00:04:26.460 --> 00:04:30.150 just log someone else 74 00:04:32.790 --> 00:04:34.123 should derive. 75 00:04:36.530 --> 00:04:40.510 Now, okay, and actually we can put the condition right here 76 00:04:40.510 --> 00:04:42.150 in the IF condition. 77 00:04:42.150 --> 00:04:44.020 So this was just to show you a little bit 78 00:04:44.020 --> 00:04:45.920 the thought process. 79 00:04:45.920 --> 00:04:47.300 But as I mentioned earlier, 80 00:04:47.300 --> 00:04:50.290 we usually create the condition right here 81 00:04:50.290 --> 00:04:52.980 in the IF statement. 82 00:04:52.980 --> 00:04:57.980 So give it a safe and now let's run it and the result is, 83 00:04:58.620 --> 00:05:01.010 someone else should drive. 84 00:05:01.010 --> 00:05:05.880 So that is because has good vision is false, 85 00:05:05.880 --> 00:05:08.720 and so our condition of has driver's license 86 00:05:08.720 --> 00:05:11.300 and has good vision is not true. 87 00:05:11.300 --> 00:05:15.140 Because it's only true in case that both of them are true, 88 00:05:15.140 --> 00:05:17.870 as you already know by now. 89 00:05:17.870 --> 00:05:20.140 So this one is false right now. 90 00:05:20.140 --> 00:05:23.770 And so therefore the else block will be executed. 91 00:05:23.770 --> 00:05:26.363 But of course, we can change it once more. 92 00:05:27.550 --> 00:05:30.570 And so right now, both of them are true. 93 00:05:30.570 --> 00:05:35.310 So has driver's license true and has good vision true. 94 00:05:35.310 --> 00:05:40.263 So true and true, is true and so Sarah is able to drive. 95 00:05:41.530 --> 00:05:45.970 Let's check that and indeed, great. 96 00:05:45.970 --> 00:05:48.510 And but this one working now perfectly, 97 00:05:48.510 --> 00:05:50.610 let's take it to the next level 98 00:05:50.610 --> 00:05:53.173 and add another Boolean variable here. 99 00:05:54.140 --> 00:05:59.133 So, let's now also add is tired. 100 00:06:01.370 --> 00:06:03.693 And let's set it to true as well. 101 00:06:04.580 --> 00:06:07.363 So we can say that this is our variable C. 102 00:06:08.340 --> 00:06:13.130 So to use more than two variables with, for example, 103 00:06:13.130 --> 00:06:16.763 the end operator, let's just go ahead and copy this one. 104 00:06:17.890 --> 00:06:20.470 So if you want to say has driver's license 105 00:06:20.470 --> 00:06:23.600 or has good vision or is tired. 106 00:06:23.600 --> 00:06:27.730 All you have to do is to add another OR operator here, 107 00:06:27.730 --> 00:06:29.730 just like you would add another plus 108 00:06:29.730 --> 00:06:31.563 or another minus operator. 109 00:06:33.270 --> 00:06:36.760 And the result of this should of course, be true, 110 00:06:36.760 --> 00:06:39.143 because while all of them are true. 111 00:06:40.810 --> 00:06:42.323 And indeed, it is. 112 00:06:43.170 --> 00:06:45.373 And if we set them all to end, 113 00:06:48.220 --> 00:06:53.037 then it is also true, because all of them are true. 114 00:06:53.037 --> 00:06:55.430 And if we set this one to false, 115 00:06:55.430 --> 00:07:00.320 then as you can guess the result will be false. 116 00:07:00.320 --> 00:07:03.100 And that is because as I explained in the last lecture, 117 00:07:03.100 --> 00:07:06.230 it's enough for one of the operands to be false 118 00:07:06.230 --> 00:07:09.673 to make the whole end operation false as well. 119 00:07:12.420 --> 00:07:16.170 Okay, but let it set back to true. 120 00:07:16.170 --> 00:07:19.990 And now, we can use this to improve our decision making, 121 00:07:19.990 --> 00:07:23.670 whether Sarah should drive or not. 122 00:07:23.670 --> 00:07:25.900 So with this third variable now, 123 00:07:25.900 --> 00:07:27.910 we want Sarah to be able to drive 124 00:07:27.910 --> 00:07:31.970 if she has a driver's license, if she has good vision 125 00:07:31.970 --> 00:07:35.460 and if she is not tired, right? 126 00:07:35.460 --> 00:07:39.010 So let's now translate that into a condition. 127 00:07:39.010 --> 00:07:40.770 And I will just copy this one 128 00:07:40.770 --> 00:07:43.820 and then comment all of it out using Command 129 00:07:43.820 --> 00:07:47.460 or Control/ just like many times before 130 00:07:48.650 --> 00:07:52.030 and now we will improve this one. 131 00:07:52.030 --> 00:07:54.500 So this one, of course, is the same 132 00:07:54.500 --> 00:07:58.180 that she needs to have a driver's license and good vision. 133 00:07:58.180 --> 00:08:02.310 But now additionally, we want her to be not tired. 134 00:08:02.310 --> 00:08:05.160 So right now she is tired, it's true 135 00:08:05.160 --> 00:08:08.460 and that's, of course, not good for driving. 136 00:08:08.460 --> 00:08:11.550 So we want the opposite of being tired. 137 00:08:11.550 --> 00:08:15.380 And so therefore, we need to invert it. 138 00:08:15.380 --> 00:08:17.080 So do you remember how that works? 139 00:08:18.360 --> 00:08:21.760 All we need to do is to use the NOT operator. 140 00:08:21.760 --> 00:08:26.520 So not is tired, all right? 141 00:08:26.520 --> 00:08:28.930 So let's read this again, 142 00:08:28.930 --> 00:08:32.770 Sarah is able to drive if she has a driver's license. 143 00:08:32.770 --> 00:08:36.290 So if this one is true, if she has good vision, 144 00:08:36.290 --> 00:08:40.120 so if this one is true and if she is not tired, 145 00:08:40.120 --> 00:08:42.313 so if all of this is true here. 146 00:08:43.420 --> 00:08:46.810 So only in this condition, Sarah is able to drive. 147 00:08:46.810 --> 00:08:50.010 Now how is this part here true? 148 00:08:50.010 --> 00:08:54.890 Well, it's true, when is tired is false, right? 149 00:08:54.890 --> 00:08:56.310 So what do you think will happen 150 00:08:56.310 --> 00:08:58.960 in this situation right now? 151 00:08:58.960 --> 00:09:01.353 Well, let's test and then analyze. 152 00:09:02.350 --> 00:09:05.790 So we get the result, someone else should drive. 153 00:09:05.790 --> 00:09:07.590 So why is that? 154 00:09:07.590 --> 00:09:09.030 Well, this one is true, 155 00:09:09.030 --> 00:09:11.750 this one is true as we see up here, 156 00:09:11.750 --> 00:09:14.880 and then is tired is also true. 157 00:09:14.880 --> 00:09:18.500 However, not is tired is false. 158 00:09:18.500 --> 00:09:20.450 So this part here is false. 159 00:09:20.450 --> 00:09:25.000 And so true and true and false is of course, false. 160 00:09:25.000 --> 00:09:27.870 And so therefore, we get the else block, 161 00:09:27.870 --> 00:09:29.860 someone else should drive. 162 00:09:29.860 --> 00:09:30.893 Now to fix this, 163 00:09:31.780 --> 00:09:36.780 we need to change is tired to false, all right? 164 00:09:37.330 --> 00:09:40.750 And so right now is tired is false 165 00:09:40.750 --> 00:09:43.850 and therefore not is tired will become true. 166 00:09:43.850 --> 00:09:47.090 And then we have true and true and true 167 00:09:47.090 --> 00:09:50.743 and then in this situation, Sarah will be able to drive. 168 00:09:51.940 --> 00:09:54.870 Yes, indeed, it works now. 169 00:09:54.870 --> 00:09:58.340 So as you see, with these three Boolean operators, 170 00:09:58.340 --> 00:10:02.410 we can model all kinds of companies decisions like this one. 171 00:10:02.410 --> 00:10:06.090 Now, I know that this was probably a bit confusing, 172 00:10:06.090 --> 00:10:07.890 but please don't worry too much, 173 00:10:07.890 --> 00:10:10.970 because it's all very confusing for everyone 174 00:10:10.970 --> 00:10:14.350 when they first learn how to program, okay? 175 00:10:14.350 --> 00:10:16.710 Just take some time after this video 176 00:10:16.710 --> 00:10:19.800 and analyze again exactly what happens here. 177 00:10:19.800 --> 00:10:22.190 Maybe also together with the last video 178 00:10:22.190 --> 00:10:23.970 to really make sure that you understand 179 00:10:23.970 --> 00:10:25.890 what is going on here. 180 00:10:25.890 --> 00:10:28.860 But of course, the best way to retain any knowledge 181 00:10:28.860 --> 00:10:31.840 is by practicing and reinforcing it. 182 00:10:31.840 --> 00:10:35.363 And so let's do that now in the next coding challenge.