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Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:02,180 --> 00:00:07,030 In the last lecture we had a look at reference of primitive types something super important to keep 2 00:00:07,030 --> 00:00:09,800 in mind when working with javascript. 3 00:00:10,030 --> 00:00:14,260 Another thing you will see quite a lot in this course are array functions. 4 00:00:14,260 --> 00:00:17,240 We already saw filter a couple of lectures ago. 5 00:00:17,350 --> 00:00:20,550 We also got sort, map and so on. 6 00:00:20,860 --> 00:00:22,670 Let me quickly show you what I mean. 7 00:00:22,810 --> 00:00:27,560 The good old numbers array with 1, 2 and 3. 8 00:00:27,970 --> 00:00:34,510 Now let's say we want to turn this into an array where each number is doubled. 9 00:00:34,540 --> 00:00:41,370 So we have to doubleNumArray, something like that we can use an array function for this. 10 00:00:41,440 --> 00:00:45,050 We can take the numbers array and call map. 11 00:00:45,130 --> 00:00:47,150 Map is a built-in array method. 12 00:00:47,170 --> 00:00:49,070 And there are many of these methods. 13 00:00:49,420 --> 00:00:51,610 I will use quite a lot of them and they're not. 14 00:00:51,610 --> 00:00:57,940 Next generation javascript all these methods work in the same way though they take a function as an 15 00:00:57,940 --> 00:01:04,750 input and this function which is an arrow function here but could be a normal function is then simply 16 00:01:04,819 --> 00:01:09,050 executed on each element in the array here. 17 00:01:09,070 --> 00:01:13,830 So on each element in the numbers array, on 1 and 2 and 3. 18 00:01:14,260 --> 00:01:18,200 So therefore what we get in this arrow function is a number in the end. 19 00:01:18,220 --> 00:01:22,260 But you can name this argument whatever you want here. 20 00:01:22,260 --> 00:01:24,400 We can then simply return something. 21 00:01:24,610 --> 00:01:30,660 And what you have to do in this internal function depends on which area of function you are using. 22 00:01:30,670 --> 00:01:37,010 Check the docs in places like d Mozilla Developer Network docs to learn more about the available array 23 00:01:37,100 --> 00:01:38,470 functions. 24 00:01:38,470 --> 00:01:44,770 So in the map function we have to return the new value we want to turn the old one into so we could 25 00:01:44,770 --> 00:01:49,440 return num * 2 and since this is executed on every element here. 26 00:01:49,450 --> 00:01:55,890 It will return 2, 4 and 6 and conveniently map all the returns a new array. 27 00:01:55,900 --> 00:02:00,720 So a real new array which is then stored in doubleNumArray. 28 00:02:01,060 --> 00:02:12,520 So now if I output numbers and thereafter doubleNumArray like this and then I'll hit run you'll see 29 00:02:12,580 --> 00:02:19,750 the old one is unchanged but the new one holds double the values and I will explain what these functions 30 00:02:19,750 --> 00:02:21,620 do when we use them in the course. 31 00:02:21,850 --> 00:02:24,590 I just want to bring them to your attention right now. 32 00:02:24,670 --> 00:02:30,730 Explain that they always have this function which gets executed on each element and that they are not 33 00:02:30,760 --> 00:02:36,190 next generation javascript but normal javascript actually, be prepared to meet them. 34 00:02:36,190 --> 00:02:41,600 I will explain what they do when we see them and always feel free to dive into docs like the Mozilla 35 00:02:41,600 --> 00:02:43,840 developer network to learn more about them. 3635

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