WEBVTT 00:01.020 --> 00:06.810 In previous lecture, we have discussed how spread operator works and now I want to introduce you new 00:06.810 --> 00:13.230 type of parameter in ethics, which is the rest from syntactic perspective, they are expressed the 00:13.260 --> 00:14.300 exact same way. 00:14.580 --> 00:19.590 We have to use three dots, but w parameter works in an opposite way. 00:20.190 --> 00:31.590 So let's create simple function costs a equals the function and insert here two parameters X and Y. 00:34.280 --> 00:40.100 Let's run in council with some of those parameters, right, council log X plus Y. 00:43.230 --> 00:54.630 Then called the function and place here more than two arguments, right, 10, 20, 30 and 40, if we 00:54.630 --> 00:58.860 rule out, then we'll get some our first and second arguments. 00:59.730 --> 01:02.790 Regardless of that, we have pushier more than two arguments. 01:03.270 --> 01:05.690 Function is working without any errors or bux. 01:06.240 --> 01:09.030 But again, we get some of only first two arguments. 01:09.600 --> 01:16.020 So actually, it's interesting how we can use the rest of the arguments in why we have special Keywood 01:16.020 --> 01:23.610 arguments, which represents arguments of function and returns array like object, its index based and 01:23.610 --> 01:24.720 has the length property. 01:25.560 --> 01:28.890 Let's at first thing counsel what arguments look like, right? 01:28.890 --> 01:31.470 Consider log arguments. 01:34.460 --> 01:39.860 That revolt and you see that we have an object which looks like an array. 01:40.340 --> 01:43.870 The items have index numbers and also it has length property. 01:45.200 --> 01:50.240 Also, as you notice, it doesn't contain only third and fourth arguments. 01:50.510 --> 01:52.270 It includes all four arguments. 01:53.600 --> 01:59.600 So in order to use third and fourth arguments and calculate the total sum, we can write the following 02:00.080 --> 02:01.220 plus arguments. 02:03.080 --> 02:07.220 And for third arguments, we have to place the index number two. 02:08.630 --> 02:13.820 Then again, plus arguments with index number three. 02:15.660 --> 02:20.070 Reload and we have 100, the sum of all the arguments. 02:21.040 --> 02:27.130 As we said, arguments is an array like object, so in order to use our methods with it, we need to 02:27.130 --> 02:28.630 transform it into array. 02:29.380 --> 02:34.120 I'm sure you remember S5 approach, which we have seen in previous videos. 02:34.630 --> 02:39.880 So we need to write a red DOT prototype. 02:41.270 --> 02:43.950 Dot, dot, dot com. 02:47.310 --> 02:53.700 So if we reload, we will get arguments collection, but in this case, as a right, I would like to 02:53.700 --> 02:56.820 note that arguments object doesn't work with our functions. 02:57.330 --> 03:06.990 If we change this regular function and right here our function, then we will get an error telling us 03:06.990 --> 03:08.750 that argument is not defined. 03:09.300 --> 03:11.470 All right, in Essex. 03:11.490 --> 03:16.980 There is no need to use arguments, objects, because new version of JavaScript allows us to use Reath 03:16.980 --> 03:20.880 parameter, which is more flexible and convenient than arguments. 03:21.480 --> 03:23.010 Let's delete those lines. 03:23.010 --> 03:25.050 And after X and Y. 03:25.060 --> 03:25.500 Right. 03:25.530 --> 03:26.750 Dot, dot, dot, dot. 03:27.810 --> 03:34.290 Actually, it's not keyword you can use here anything you want, like, for example, arguments or something 03:34.290 --> 03:34.640 else. 03:35.640 --> 03:38.640 But remember that using three dots is always mandatory. 03:39.660 --> 03:42.420 That's the first thing Castlebar about this parameter gives us. 03:42.420 --> 03:42.780 Right. 03:42.790 --> 03:44.460 Cancel that log rest. 03:47.590 --> 03:54.190 So as you see, it returns an array, but only with two arguments, third and fourth, which actually 03:54.190 --> 03:55.780 are missed as parameters. 03:56.890 --> 04:07.690 And in order to gather some of these arguments, we have to write X plus Y plus rest with index number 04:07.690 --> 04:13.720 zero and then plus rest with index number one. 04:16.630 --> 04:19.540 So we have, again, total sum of arguments. 04:20.520 --> 04:25.770 All right, let's use another example and see better the power of parameter. 04:26.910 --> 04:28.560 Create consent family. 04:31.180 --> 04:37.260 Suppose that we would have several members of family, those persons would have common last name. 04:37.270 --> 04:40.450 So let's place you as a first parameter. 04:40.450 --> 04:41.140 Last name. 04:43.580 --> 04:50.150 And then let's assume that as arguments, we would have names of family members for that, I'm going 04:50.150 --> 04:52.040 to use a rest parameter, so. 04:52.040 --> 04:54.050 Right, dot, dot, dot names. 04:56.510 --> 05:01.590 Then use erode function because of that the parameter returns array. 05:01.970 --> 05:06.480 Therefore, I'm going to use a Ray Hopper method for each and using this method. 05:06.500 --> 05:09.940 We will define first names and last names for each family member. 05:10.580 --> 05:11.000 So. 05:11.000 --> 05:11.420 Right. 05:11.420 --> 05:13.700 Names for each. 05:14.700 --> 05:21.510 Then as the current item right name, which is followed by eral function. 05:25.150 --> 05:27.430 And then running castle. 05:30.250 --> 05:31.510 Name and. 05:32.970 --> 05:33.690 Last name. 05:35.280 --> 05:36.690 Using tablet strength. 05:40.110 --> 05:48.060 All right, let's invoke dysfunction right below family for the last time, I'm going to insult your 05:48.060 --> 05:55.260 argument as, for example, Smith and for names of our family members. 05:55.920 --> 06:01.350 Let's place your neck then, Jane. 06:03.650 --> 06:04.130 Bob. 06:05.930 --> 06:07.220 And Jessica. 06:09.960 --> 06:11.160 Let's reload the page. 06:12.370 --> 06:18.130 And you said that we have here persons with different names, but with common last name, Smith. 06:18.430 --> 06:18.880 All right. 06:19.330 --> 06:23.300 So you see how convenient and also how simple is to use race parameter. 06:23.950 --> 06:30.190 Also, you need to remember that we always have to place a parameter at the end inside parentheses. 06:31.270 --> 06:37.180 It doesn't matter how many arguments you will have, a parameter will work with all arguments which 06:37.180 --> 06:39.460 are not represented with parameters. 06:40.480 --> 06:43.740 OK, it was all about race parameter in Essex. 06:44.050 --> 06:45.250 See you in the next video.