WEBVTT 00:01.170 --> 00:07.110 You already know that in JavaScript we have function statements and function expressions in case of 00:07.110 --> 00:13.320 function expressions, you're able to assign function as a value to the variable and then invoke it 00:13.320 --> 00:14.360 using variable name. 00:15.120 --> 00:19.110 It's because functions in JavaScript are first class functions. 00:20.250 --> 00:25.710 So I'm not going to repeat again what function expressions are because you already know well how they 00:25.710 --> 00:26.030 work. 00:26.400 --> 00:32.760 I'm just going to show you real power of JavaScript functions which actually act in different ways than 00:32.760 --> 00:34.380 in many other programming languages. 00:35.040 --> 00:37.200 So what are first class functions? 00:38.280 --> 00:45.600 This concept means the following that in JavaScript we are able to store function in a variable we can 00:45.600 --> 00:53.490 use function as a variable, also pass them as parameters and we are able to return function from other 00:53.490 --> 00:56.790 function in many other programming languages. 00:56.800 --> 01:00.060 We are not allowed to use functions in such flexible ways. 01:01.560 --> 01:04.280 All right, let's see exactly what I'm talking about. 01:05.010 --> 01:11.160 So as we said, we can store functions in variables that's demonstrated once again, we need to create 01:11.160 --> 01:13.710 variable and assign to it anonymous function. 01:13.710 --> 01:14.280 So right. 01:14.280 --> 01:18.120 VAR A equals to anonymous function. 01:21.130 --> 01:22.690 And then right, counsel Deathlok. 01:24.120 --> 01:24.540 Hello. 01:28.670 --> 01:35.270 In order to invoke it, we can use the name of the variable and we need to write it after verbal declaration 01:35.270 --> 01:40.430 because of the hoisting, if we invoke it before it's declaration. 01:42.760 --> 01:45.030 Then we will get an error. 01:46.030 --> 01:49.910 Because as we already know, the value of the variable A is undefined. 01:51.220 --> 01:54.430 OK, it was just for reminding some important things. 01:55.120 --> 02:03.940 Let's write another example and remove this code, create function and call it some. 02:05.570 --> 02:06.800 Inside the parentheses. 02:07.760 --> 02:12.080 Let's consider the parameters, number one and number two. 02:14.930 --> 02:21.950 And now I'm going to pass here a third parameter, which I will use then as a function, I mean that 02:21.950 --> 02:26.660 when we invoke function some, we will pass this function as an argument. 02:27.290 --> 02:28.520 So right here from. 02:30.300 --> 02:34.680 Then in council, that's ad number one and number two, right? 02:35.000 --> 02:36.540 Good luck, number one. 02:36.540 --> 02:38.220 Plus number two. 02:40.500 --> 02:47.110 Then write another consider log in, which I'm going to invoke function, which is passed as a parameter. 02:47.700 --> 02:48.870 So right here and. 02:51.330 --> 02:56.580 OK, let's invoke function some rule that we need to write some. 02:58.520 --> 03:08.960 And then pass arguments for number one and number two as five and 10, and now I'm going to pursue as 03:08.960 --> 03:10.730 an argument, anonymous function. 03:11.270 --> 03:21.260 So right to function and then inside the coal prices return statement and write function is executed. 03:26.370 --> 03:35.730 Reload and you see that we have 15 and that function is executed, so you see that we have post function 03:36.120 --> 03:38.640 as a parameter for another function. 03:39.610 --> 03:40.060 OK. 03:41.380 --> 03:47.740 As we said, we can use function as a variable, and in order to do that, we can define this function 03:47.740 --> 03:48.390 outside. 03:48.910 --> 03:50.890 Let's cut it from here and. 03:52.480 --> 03:56.440 Paste, then call it as done. 03:58.560 --> 04:04.740 And then as an argument, we need to pass your name of the function as variable 04:07.380 --> 04:13.260 reload, and you said that we have again, 15 and function is executed. 04:14.830 --> 04:21.910 All right, in order to make our election more interesting, I'm going to write another a bit complicated 04:21.910 --> 04:22.480 example. 04:24.430 --> 04:30.640 Suppose that we have an array which consists of scores of students so. 04:30.640 --> 04:31.060 Right. 04:31.060 --> 04:46.210 Of course, equals and plus here, some numbers, 55, then 35, 87, and let's say 45. 04:48.830 --> 04:54.650 Now we need to create a function which will check if a particular student could pass an exam. 04:55.550 --> 04:59.930 Keep in mind that the limit of passing exam is 51 points. 05:01.310 --> 05:07.490 Recently, I have shot the example like this, but in this case, I'm going to tweet function as first 05:07.490 --> 05:08.180 class function. 05:08.840 --> 05:17.320 So write your function and call it check result inside the parentheses. 05:17.330 --> 05:24.680 I'm going to pass parameters first one for array and the second one for function. 05:26.570 --> 05:32.930 Then inside the the braces create another array which will be empty for now because I'm going to add 05:32.930 --> 05:34.580 in that array results. 05:35.120 --> 05:42.170 So write a new array equals to empty square brackets. 05:45.190 --> 05:51.190 In order to check a particular score, we need to look through the array items for that, I'm going 05:51.190 --> 05:52.240 to use for a loop. 05:52.240 --> 05:53.170 So right for. 05:54.930 --> 05:57.180 Then variable I equal to zero. 05:59.220 --> 06:03.330 Then we need I is less than I write at length. 06:06.400 --> 06:15.160 And then the increment I plus plus, OK, in order to add items, the new empty array, you remember 06:15.160 --> 06:17.560 that we need to use a right push method. 06:18.250 --> 06:21.520 So right newera that push. 06:25.440 --> 06:31.980 And in a moment of adding items, we need to invoke function, which was passed as a parameter here, 06:32.940 --> 06:37.470 as an argument for the function, we need to pass current item from the array. 06:38.280 --> 06:48.320 So right then and inside the parenthesis right away and in square brackets indicate the variable. 06:49.530 --> 06:53.150 And after that, in order to get a new era, we need to return it. 06:53.190 --> 06:53.420 So. 06:53.430 --> 06:53.730 Right. 06:53.910 --> 06:55.470 Return a new array. 06:57.650 --> 06:58.070 OK. 06:59.400 --> 07:05.970 Now, let's write function, which will actually check if a student could pass an exam and then this 07:05.970 --> 07:10.860 function will be passed as an argument when we call check result function. 07:11.520 --> 07:16.590 So write function and call it pass or fail. 07:18.900 --> 07:26.640 As you see, we have passed your parameter, which points to current item, and now we need to indicate 07:26.640 --> 07:27.900 it here as an argument. 07:28.770 --> 07:30.200 Let's call it score. 07:32.990 --> 07:40.190 In order to pass the exam, the current score should be great or equal to 51, so let's write it. 07:40.940 --> 07:47.420 Return score is greater than or equal to 51. 07:48.570 --> 07:52.350 All right, now it's time to check results function. 07:53.650 --> 07:57.790 Write it in console console that lock check result. 08:00.540 --> 08:06.580 So this function has two parameters, array and function as an array. 08:06.600 --> 08:15.030 We need to process course and as function, we need to use pass or fail function that we have just created. 08:18.950 --> 08:27.770 Reload and you see that we have a right which consists of boolean values, true value means that score 08:27.800 --> 08:32.870 was greater or equal to 51 and the student could pass an exam. 08:33.530 --> 08:36.680 And in case of false, the student was failed. 08:38.570 --> 08:39.110 All right. 08:40.930 --> 08:46.330 We can create multiple functions, which will give us other information about the result of the exam, 08:46.690 --> 08:52.930 for example, if we want to define what was the difference between the limit and the actual scores, 08:53.440 --> 08:54.870 we can create another function. 08:55.150 --> 08:56.740 So right function. 08:57.750 --> 09:08.940 And call it calculate difference that inside the parenthesis, right, score again and as a written 09:08.940 --> 09:13.170 statement, we need to write a score minus fifty one. 09:17.540 --> 09:23.990 Then duplicated and changed the name of the function into calculate difference. 09:26.890 --> 09:35.110 Reload, and so here we have another array, which consists of differences between 51 and the actual 09:35.110 --> 09:35.560 scores. 09:37.070 --> 09:39.520 OK, it's nice, right? 09:40.030 --> 09:46.690 Using functions as first class functions is a big advantage of JavaScript because they are very flexible 09:46.690 --> 09:50.680 and convenient way to write really nicely structured code. 09:52.370 --> 09:53.680 All right, let's move on.