WEBVTT 00:01.270 --> 00:06.550 Let's talk about another era helper method, which is map, as it was in case the forage method, I'm 00:06.550 --> 00:08.640 going to compare map helper to follow. 00:10.600 --> 00:17.740 Suppose that we have an array which consists of some numbers, so create variable numbers and insert 00:17.740 --> 00:21.760 here numbers from, for example, one to five. 00:23.930 --> 00:30.260 Then suppose that we want to multiply each of these numbers to ten, keep each iteration and result 00:30.260 --> 00:33.080 in a new era without changing the original one. 00:33.800 --> 00:36.980 So let's create an empty array and call it new array. 00:39.580 --> 00:48.100 And then let's use for a loop to iterate through the numbers, right, for I equals to zero, then I 00:48.100 --> 00:54.250 is less than the length of numbers array and then I plus plus. 00:55.630 --> 01:02.470 So in order to add results in new array, I'm going to use known array method called push, which adds 01:02.470 --> 01:04.630 new item into array as a last one. 01:05.050 --> 01:07.960 So right now you are right that push. 01:09.790 --> 01:19.420 And inside the parenthesis right numbers, I multiplied to 10, as we said, we want to create new array 01:19.420 --> 01:22.400 and keep the original one at the same time. 01:22.780 --> 01:24.850 So let's look both of them in cancel. 01:24.880 --> 01:25.270 Right. 01:25.270 --> 01:26.200 Cancel the log. 01:27.460 --> 01:27.970 No. 01:29.840 --> 01:32.090 And then consider that look, New Arite. 01:35.490 --> 01:36.050 Reload. 01:36.180 --> 01:40.830 And here we go, we have original array and the new era with new items. 01:41.940 --> 01:42.360 All right. 01:42.750 --> 01:48.420 It's one of the ways to reach this results, but we can do the same, but in a much simpler and easier 01:48.420 --> 01:48.630 way. 01:48.630 --> 01:52.200 Using Map Hopper, let's again make here some border. 01:55.070 --> 02:03.020 I'm going to create a new variable and store the results into this variable, so let's call it map array. 02:04.590 --> 02:09.630 Which equals to numbers and use here MUP Harper. 02:11.020 --> 02:15.640 Syntax is very similar to forage method, we need to pursue an anonymous function. 02:17.950 --> 02:23.560 And then let's pass as a parameter number in singular form, as it was previously. 02:26.030 --> 02:31.250 All right, it's very important to remember that always when we deal with error happens, we need to 02:31.250 --> 02:32.570 use a statement. 02:33.090 --> 02:35.510 The right return, no. 02:37.080 --> 02:38.550 Multiplied to 10. 02:42.420 --> 02:46.440 Let's say in council, what we have looked at first, the original numbers are right 02:49.260 --> 02:52.950 and then newly created variable, not a rate. 02:56.210 --> 02:56.720 Revote. 02:57.230 --> 03:03.290 And here we go, we have the exact same result as it was in case of Falbe, but in this case, you notice 03:03.290 --> 03:07.160 very clearly that the amount of code is much less than in previous case. 03:07.700 --> 03:10.160 We got the same result in much more simple way. 03:10.160 --> 03:16.220 And the most important thing to note is that you realize at a glance that logic is much more simple 03:16.220 --> 03:17.120 to understand. 03:18.560 --> 03:23.960 Again, you must keep in mind always to use a written statement, because if we miss it. 03:24.930 --> 03:27.900 Then the function will give us the values as undefined. 03:30.330 --> 03:34.620 All right, let's take a look on how map Harper actually works behind the scenes. 03:35.580 --> 03:42.390 Here we have our original array of numbers, then another array which is created using Map Harper and 03:42.390 --> 03:43.320 the function itself. 03:44.100 --> 03:50.910 So at first function is executed for first item one is multiplied to ten and the result is added to 03:50.910 --> 03:51.780 an empty array. 03:52.710 --> 03:58.560 Then function is executed for second item, which is two, it's multiplied to ten and the result is 03:58.560 --> 03:59.960 added two new array as well. 04:00.780 --> 04:09.960 And in the same way function is executed for the item, then for fourth item and for last item, which 04:09.960 --> 04:10.530 is five. 04:11.160 --> 04:15.010 And all the results are added to a new array again. 04:15.030 --> 04:21.210 Remember that when we use Matara Helper, the original array is maintained as immutable, which means 04:21.210 --> 04:22.350 that it's not changed. 04:23.600 --> 04:24.230 Makes sense. 04:25.010 --> 04:25.460 All right. 04:26.460 --> 04:32.760 Let's writes one more example, suppose that we have an array of persons which consists of several objects 04:32.760 --> 04:42.420 with properties, force them in last name, so create variable persons, then insert in its object with 04:42.420 --> 04:42.930 properties. 04:42.930 --> 04:44.640 First name John 04:47.280 --> 04:48.570 and last name Smith. 04:50.730 --> 04:56.130 Let's duplicate it twice and then change the values of properties, writes Bob. 04:58.430 --> 04:59.270 Then Brown. 05:02.620 --> 05:05.860 And the third one, Nick and Dought. 05:08.640 --> 05:14.120 Now, suppose that we want to group first names in you arrange for that, the perfect way is to use 05:14.420 --> 05:15.230 a right helper. 05:15.600 --> 05:18.990 So let's create a variable, get first names. 05:21.300 --> 05:29.250 Which equals to persons that Matt Puscifer, again, a function with parameter. 05:30.380 --> 05:30.980 Person. 05:34.370 --> 05:40.460 As we said, we are going to group first names of those objects, so we need to return the person that 05:40.880 --> 05:41.600 first name. 05:45.340 --> 05:48.820 So everything is ready, let's make again here little line. 05:53.700 --> 05:59.190 And then, look, both variables in console, right, console the clock persons. 06:00.790 --> 06:03.970 And then cancel the luck, get first names. 06:06.350 --> 06:06.910 Reload. 06:07.910 --> 06:13.460 And here we have our original persons array and then you array, which consists of first names of the 06:13.460 --> 06:19.700 objects, you can try the same with follow and you will be ensured that map is much more convenient 06:19.700 --> 06:23.840 and fast way to set up the same logic and get the same result. 06:24.920 --> 06:26.600 All right, let's go ahead.