WEBVTT 00:01.010 --> 00:07.580 So we have finished considering our helpers, and now it's time to actually start describing updated 00:07.580 --> 00:11.660 and new features of JavaScript, which are represented in its version. 00:12.690 --> 00:19.800 Generally, I would like to note that there was almost nothing in ECMAScript 2015 or ESX version that 00:19.800 --> 00:21.570 could not be done using S5. 00:22.230 --> 00:27.960 So because of that, throughout this section, in most cases we will compare year five and six code 00:27.960 --> 00:28.560 to each other. 00:29.540 --> 00:35.060 The first thing that we're going to discuss is the most popular change in ethics, which is variable 00:35.060 --> 00:38.500 declaration, you already know how to declare variable. 00:38.840 --> 00:40.760 We have done it dozens of times. 00:41.330 --> 00:43.160 For that, we need to use keyword war. 00:44.150 --> 00:45.560 With name and value. 00:49.390 --> 00:49.840 Let's. 00:51.030 --> 00:52.620 Look them in council. 00:56.570 --> 00:58.910 So here we have John and 28. 01:00.210 --> 01:05.880 In year five, we are able to change dynamically values of the variables, for example, if we assign 01:05.880 --> 01:11.820 to name and age variables the other values like Nick and. 01:13.550 --> 01:15.260 29 to age. 01:16.860 --> 01:19.300 Then they will be dynamically changed. 01:20.040 --> 01:25.710 This stuff is different in year six and let's see how it actually works in new version of JavaScript. 01:25.740 --> 01:32.550 There are two types of variable declarations left and cost where we want to update the content of variable 01:32.550 --> 01:33.270 dynamically. 01:33.690 --> 01:39.870 We should use keyword LAT, but if we want to never change the content of the variable, then we have 01:39.870 --> 01:43.220 to use const, which actually stands for constant. 01:44.010 --> 01:47.490 In this case, I'm going to declare any variable with const. 01:48.400 --> 01:52.150 Because you agree that in most cases the name of the person never changes. 01:52.480 --> 01:54.740 As for the age, it's definitely changed. 01:54.790 --> 01:57.020 Therefore, I'm going to declare it with LET. 01:57.730 --> 02:02.890 Actually, this is the main and the only difference between that and declarations. 02:03.850 --> 02:04.300 All right. 02:04.870 --> 02:11.290 Let's reload the page and you see that we have an error and the problem is an assignment to constant 02:11.290 --> 02:11.760 variable. 02:12.370 --> 02:17.760 So as we said, when you assign the value to constants variable, then you can never change it. 02:17.980 --> 02:22.450 It doesn't matter if you write your neck or its initial value, John. 02:23.370 --> 02:25.590 Anyway, we will get an error. 02:26.680 --> 02:29.950 So you cannot use assignment operator. 02:30.400 --> 02:33.970 I mean, equals sign with the same constant variable twice. 02:35.360 --> 02:41.150 OK, as for the constant variable, I would like to note that recently there was a special convention 02:41.150 --> 02:41.840 in JavaScript. 02:42.200 --> 02:48.230 If developers wanted to never change the values of variables for that, they were using capital letters 02:48.230 --> 02:50.060 with variable names like this. 02:53.510 --> 02:54.050 All right. 02:55.180 --> 02:57.280 Let's delete this line of code. 02:58.270 --> 03:07.360 Reload and we have John and 29, so in case of that variable, we do not have any problem with updating 03:07.360 --> 03:08.590 the value of the variable. 03:09.340 --> 03:14.940 At a glance, it seems that that declaration works exactly as VAR Declaration does. 03:15.400 --> 03:20.770 Actually, I can tell you that they work in a similar way, but there are some differences between those 03:20.770 --> 03:21.460 declarations. 03:22.150 --> 03:23.920 All right, let's remove this code. 03:25.230 --> 03:30.960 So as we know, in year five, we can create a variable, for example, person. 03:32.340 --> 03:35.310 And assigned to its value, John Smith. 03:36.960 --> 03:42.810 And then using the same verbal name, we can overwrite new value to old one. 03:45.400 --> 03:48.190 So if we check in councilperson variable. 03:49.250 --> 03:51.080 Of course, we will get to. 03:52.400 --> 03:56.720 Let's see what happens in Essex, change of our keyboards into let. 03:58.930 --> 04:05.460 That revolt and you see that we have an error, which tells us that person has already been declared 04:05.650 --> 04:10.710 so which means that in Essex you are not able to overwrite value of the same variables. 04:11.080 --> 04:16.000 And actually, it's really helpful and great picture because in practice, when you deal with large 04:16.000 --> 04:19.990 code, it will allow us to avoid naming conflicts with variables. 04:21.030 --> 04:27.750 All right, let's talk about another difference between that and Hvar, that's the latest line of code 04:28.260 --> 04:30.660 and change that into VAR. 04:32.320 --> 04:33.730 And running council. 04:34.910 --> 04:36.920 Rite Aid before its declaration. 04:40.560 --> 04:46.350 So you see that we have undefined because of hoisting, and I'm sure that you remember what hoisting 04:46.350 --> 04:49.200 think is if we change over into that. 04:51.070 --> 05:00.130 And as a result, we have an error saying that person is not defined, so JavaScript engine, instead 05:00.130 --> 05:03.360 of undefined directly gave us an error. 05:03.490 --> 05:05.140 And in my opinion, it's better. 05:05.680 --> 05:11.590 Actually, JavaScript engine knows that there exists this variable, but it doesn't allow us to richet. 05:12.130 --> 05:14.860 This is known as temporal, that zone. 05:15.310 --> 05:19.330 It's not actually official term, but most developers use it. 05:20.480 --> 05:24.650 We will get absolutely the same results if we use constant instead of that. 05:28.800 --> 05:35.660 All right, that's the latest Cote's I want to show you one more difference between left and cost. 05:36.000 --> 05:41.910 Many developers actually do not mention it, but I want to refer to it as we remember, when we create 05:41.910 --> 05:47.280 variable on global level, it actually is stored as a property of global window object. 05:47.940 --> 05:51.000 So if we write for a equals the 10. 05:54.320 --> 05:56.060 And then check the window object. 06:00.310 --> 06:03.260 We will find variable as it's property. 06:04.450 --> 06:10.390 Also, if we write we know dot a, then we will get time. 06:11.140 --> 06:14.780 Let's see what happens in case of that and constant change. 06:14.890 --> 06:16.000 Varin into that. 06:17.410 --> 06:20.320 That reload and check again window object. 06:22.710 --> 06:28.920 You see that we cannot find here a also if we write window dot a. 06:30.510 --> 06:32.250 That we will get undefiled. 06:33.450 --> 06:37.050 The exact same happens if we use constant instead of let. 06:42.530 --> 06:47.120 I won't be sold as a property of global we don't object and also. 06:48.180 --> 06:49.350 Window dot a. 06:51.650 --> 06:53.330 Will give us defined. 06:54.290 --> 07:01.430 So in its sixth version, let and cost variables declared on global level are not stored as properties 07:01.430 --> 07:07.580 of global window object, but regardless of that, they act as global variables if they are declared 07:07.580 --> 07:10.350 on global level like it's in case of vah. 07:11.030 --> 07:11.510 All right. 07:11.870 --> 07:15.800 Let's go ahead and talk about the main difference between Vialet and cost. 07:16.640 --> 07:20.180 As we know in is five variables are functions skulked. 07:20.660 --> 07:22.040 Let's recall what it means. 07:22.430 --> 07:27.380 Creates Function A and inside Kurla prices. 07:28.730 --> 07:29.640 A variable be. 07:30.870 --> 07:32.160 With the value, hello. 07:34.400 --> 07:39.200 And then outside of function, run in council, the barrier will be. 07:41.380 --> 07:46.640 If we reload, we will get an error, which tells us speed is not defined. 07:47.620 --> 07:53.380 So in this case, verbal B is a function scope and we cannot access on it from outside function. 07:54.280 --> 07:55.840 The same happens with LET. 07:58.850 --> 08:01.580 And also with constant. 08:03.280 --> 08:05.830 In both cases, we have is not defined. 08:06.810 --> 08:13.040 So let's add cost variables are functions coped as well, but at the same time, they're blocks coalbed 08:13.110 --> 08:18.420 variable declarations and it's the main difference between Vah and Letton constant. 08:18.630 --> 08:20.580 Let's see what this exactly means. 08:20.580 --> 08:23.250 Delete this function and create if statement. 08:24.330 --> 08:27.270 And as a condition, let's just insert here through. 08:29.530 --> 08:33.310 That inside culebras is a variable for steam. 08:34.780 --> 08:36.820 And assigned to it to value John. 08:39.650 --> 08:43.910 Then run it in council from outside if statement. 08:47.590 --> 08:50.240 Revolt, and, of course, it works. 08:50.530 --> 08:51.680 We have John here. 08:52.120 --> 08:53.920 If we change over into that. 08:56.150 --> 08:56.960 That remote. 08:58.510 --> 09:02.710 You see that we have an error saying that first name is not defined. 09:03.930 --> 09:07.320 The same will happen if we use Carlstadt instead of that. 09:11.170 --> 09:17.710 So, as we said, let in constant variables are blocks kept in block, I mean, everything that is surrounded 09:17.710 --> 09:18.960 by color braces. 09:19.360 --> 09:25.600 So if we create outside of if statements variable first name using that declaration. 09:28.490 --> 09:35.920 That we will have Nic in council, regardless of that, those variables have the same names, first 09:35.930 --> 09:38.900 name, they are completely different variables. 09:40.320 --> 09:43.770 If we run inside block first name in Castle. 09:47.710 --> 09:53.020 Then we will get John and Nick, so it means that those are different variables. 09:53.890 --> 09:54.400 All right. 09:55.610 --> 10:01.160 The next thing that I want to show you is that in case of that declaration, we are able to declare 10:01.160 --> 10:05.170 it outside of block and then assign the value inside block. 10:05.600 --> 10:12.470 So if we just get rid of inside, block the let keyboard and also delete this constant dialogue, then 10:12.980 --> 10:16.400 we will get the updated value of variable first name as John. 10:17.750 --> 10:19.340 But in case of constant. 10:21.350 --> 10:26.540 We cannot do that because we cannot we assign to concepts variable, new value. 10:27.650 --> 10:33.980 But in case of consent, there was one exception when we deal with objects, let's change back constantly 10:33.980 --> 10:40.040 to that and create new objects with constant declaration, right person. 10:40.580 --> 10:47.630 And in 30 years, some properties name as Jane and then the age as 18. 10:49.440 --> 10:54.720 Then if statements change the value of age property and make it 19. 10:55.700 --> 10:58.640 And then running castle person object. 11:01.000 --> 11:09.160 You see that the value of property is changed from 18 to 19, so when we use the declaration with objects, 11:09.610 --> 11:13.150 we can manipulate all the values of the properties of that object. 11:14.260 --> 11:14.880 Makes sense. 11:16.610 --> 11:17.060 All right. 11:18.320 --> 11:25.250 Now I'm going to demonstrate what happens when we deal with a loop's, so create simple for loop, right? 11:25.250 --> 11:32.360 Verbal eye equals zero, then as a condition I'm going to write your eye is less than five. 11:33.410 --> 11:35.270 And then the increment I plus plus. 11:36.430 --> 11:39.600 Inside Collaborationists, that's Log-in Castle. 11:40.150 --> 11:40.480 I. 11:42.720 --> 11:50.600 Let's reload and we have numbers from zero to four in case of our declaration, we are able to access 11:50.700 --> 11:52.610 variable from outside of volume. 11:53.040 --> 11:55.770 So if we write, cancel that log, I. 11:58.270 --> 12:00.580 Then we will get five. 12:01.900 --> 12:08.440 If you expected four or something else instead of five, I would like to remind you that after a situation 12:08.950 --> 12:12.850 I is increased to five, condition became false. 12:13.510 --> 12:19.630 So Loopt has stopped execution and that's why the value of variable AI has been maintained as five. 12:21.350 --> 12:23.920 All right, let's change of our intellect. 12:26.400 --> 12:27.000 Revolt. 12:28.070 --> 12:34.400 And you see that at first we have numbers from zero to four, that's because of first class Deathlok, 12:34.700 --> 12:38.130 which is placed inside block, but then we have an error. 12:38.300 --> 12:44.680 And the reason is that from outside of Falbe, we cannot access unlet because it's blocks code. 12:44.690 --> 12:50.110 And for a look like a false statement and functions also creates block. 12:50.630 --> 12:51.130 All right. 12:51.800 --> 12:57.070 When we use that declaration on each iteration, new variable is created. 12:57.080 --> 13:00.800 And in order to prove that, I'm going to change slightly this example. 13:01.810 --> 13:07.450 In JavaScript, we have built in a method called Septime Out, which actually works in almost a similar 13:07.450 --> 13:09.010 way as set integral method. 13:09.460 --> 13:15.700 The difference is that it executes function once after delite set time out method texte parameters. 13:16.390 --> 13:22.420 First one is callback function and the second one is amount of time, which actually defines delay before 13:22.420 --> 13:25.930 function is executed and it's expressed in milliseconds. 13:26.710 --> 13:27.130 So. 13:27.130 --> 13:27.460 Right. 13:27.460 --> 13:32.080 Set time out then insert anonymous function. 13:34.750 --> 13:38.590 Then place this castle, that log in the braces. 13:40.390 --> 13:46.840 In order to see better how Falbe works and how each iteration is done as a second parameter, I'm going 13:46.840 --> 13:50.050 to place here, I multiplied. 13:51.060 --> 13:56.730 Two, 500 milliseconds and also change led into VAR. 13:58.270 --> 13:59.920 Delete this cancel log. 14:02.000 --> 14:02.600 Reload. 14:03.540 --> 14:10.740 And he said that we have No five, five times that happens because one function is invoked at this moment 14:10.740 --> 14:12.260 for a loop is already finished. 14:12.780 --> 14:14.670 The value of verbal is five. 14:14.670 --> 14:18.230 And because of the delay, we get it five times. 14:19.170 --> 14:23.220 Let's change over into that and see what happens. 14:24.390 --> 14:28.300 You see that numbers are apart from zero to four. 14:29.010 --> 14:30.280 It's kind of strange, right? 14:31.080 --> 14:34.580 So let me explain what has happened here in case of that variable. 14:35.130 --> 14:36.840 We know that it's blocks called. 14:37.320 --> 14:40.640 So on each iteration, new variable is created. 14:41.340 --> 14:46.130 So on each function execution, there are different variables. 14:46.590 --> 14:53.490 And what you see here, I mean, numbers from zero to four, those are values of five different variables. 14:54.670 --> 14:55.350 Makes sense. 14:57.050 --> 15:03.440 All right, you may wonder what happens if we use customs instead of let some of you may think that 15:03.440 --> 15:09.470 because of that, after each iteration new variable is created, logically, we should get the same 15:09.470 --> 15:09.860 results. 15:10.430 --> 15:11.510 Let's see what happens. 15:11.510 --> 15:13.190 Change that into cost. 15:15.430 --> 15:18.960 And you see that we have an error and also zero. 15:19.580 --> 15:23.630 So this error is cost because we cannot modify the value of constant. 15:24.290 --> 15:26.180 Initially, its value is zero. 15:26.570 --> 15:28.780 On first iteration, it gives us zero. 15:29.210 --> 15:31.090 That's why we see in Council zero. 15:31.760 --> 15:38.540 But at the end of the first iteration, when the JavaScript engine sees a plus plus, you know, that's 15:38.540 --> 15:42.460 a plus plus is the same as I equals to I plus one. 15:42.950 --> 15:49.340 So which means that assignment operator comes into play and because of that we are not able to assign 15:49.700 --> 15:51.430 new value to cost variable. 15:51.980 --> 15:54.190 That's the reason why we have an error here. 15:55.070 --> 15:55.700 Make sense. 15:57.100 --> 16:01.360 All right, before we finish this lecture, I'm going to show you one more thing. 16:02.170 --> 16:09.340 So as you remember, in year five, we could create blocks for data privacy using immediately invoked 16:09.340 --> 16:10.420 function expressions. 16:11.140 --> 16:13.600 We have seen it clearly in our quiz application. 16:14.170 --> 16:20.440 In order to create APHIS, we have to open parentheses then right function. 16:22.570 --> 16:27.580 Then inside collaborationist, let's create variable A, which equals to 10. 16:29.740 --> 16:36.100 Then invoked the function and outside of function, right, consider log a. 16:38.680 --> 16:44.800 Of course, we have an error because we cannot get access on variable aid from outside Effi, but in 16:44.800 --> 16:47.510 Essex this stuff became much more simpler. 16:48.040 --> 16:51.220 We don't need to create, if it's anymore for creating blocks. 16:51.610 --> 16:53.660 We have just to use Calabrese. 16:55.150 --> 17:05.320 And let's create here, let's be which equates to, for example, 30, if we run it in council from 17:05.320 --> 17:06.370 outside of block. 17:07.390 --> 17:14.310 Then we will get an error because we cannot access a variable, be from outside of block, obviously 17:14.350 --> 17:16.690 the same happens with constant declaration. 17:19.360 --> 17:21.190 You see that again, we have an error. 17:22.190 --> 17:25.130 But there is one thing to note, if we use your. 17:26.720 --> 17:34.940 Vaki, but than those curly braces won't work because, again, verticalization is not Bloks called. 17:36.180 --> 17:43.560 All right, after all of this stuff, you may have a question when and where to use Örvar Let or concerned 17:44.130 --> 17:51.000 some of the developers are coming to use a in cost and ignore the declaration if you write ethics code. 17:51.450 --> 17:57.380 But some of them recommend the use of our declaration only in case of declaring global variables. 17:58.350 --> 18:04.980 I suggest to use Latin counts and ignore our declaration when you writing ethics, but it's up to you, 18:04.980 --> 18:11.700 you can take into account both recommendations also generally use constant declarations in most cases. 18:12.090 --> 18:17.820 But when you know that you would have to update dynamically values of variables that always declare 18:17.820 --> 18:18.960 them using that. 18:20.460 --> 18:22.080 All right, that's it. 18:22.350 --> 18:23.540 See you in the next video.