1 00:00:01,170 --> 00:00:04,430 Let's do the opposite of the last lecture 2 00:00:04,430 --> 00:00:07,943 and create a function that returns a new function. 3 00:00:09,640 --> 00:00:14,163 So I'm gonna write a very simple greet function here, 4 00:00:15,740 --> 00:00:19,800 because this is really just to demonstrate this point here 5 00:00:19,800 --> 00:00:21,833 as easily as possible. 6 00:00:23,120 --> 00:00:27,590 So here we can pass in a greeting like hi 7 00:00:27,590 --> 00:00:30,890 or hello or something like that. 8 00:00:30,890 --> 00:00:33,018 And then all this function will do 9 00:00:33,018 --> 00:00:35,920 is to return a new function. 10 00:00:35,920 --> 00:00:36,950 So as always, 11 00:00:36,950 --> 00:00:40,973 we write return and then simply a new function value. 12 00:00:43,010 --> 00:00:45,020 And this new function that we return 13 00:00:45,020 --> 00:00:48,266 will also have a parameter so it will be able 14 00:00:48,266 --> 00:00:50,743 to receive arguments. Right? 15 00:00:51,770 --> 00:00:54,033 And so what this function here will do, 16 00:00:55,290 --> 00:00:57,540 is it will simply look to the console, 17 00:00:57,540 --> 00:01:01,170 basically the greeting, and then the name of the person 18 00:01:01,170 --> 00:01:03,273 that we passed into this function. 19 00:01:04,940 --> 00:01:06,310 So let's just write this 20 00:01:06,310 --> 00:01:08,973 and it will make sense when we see this in action. 21 00:01:10,210 --> 00:01:12,853 I'm sure it looks a bit weird right now. 22 00:01:13,890 --> 00:01:16,483 And now let's actually use the greet function. 23 00:01:18,180 --> 00:01:20,260 So let's say greet 24 00:01:21,350 --> 00:01:25,450 with hey and so 'hey' is the greeting here. 25 00:01:25,450 --> 00:01:29,940 Now what will be the result of this function call? 26 00:01:29,940 --> 00:01:34,290 Well, it's gonna be this function, right? 27 00:01:34,290 --> 00:01:39,080 And so let's store the result of this function call, 28 00:01:39,080 --> 00:01:41,913 which will be as we just said, that function, 29 00:01:43,420 --> 00:01:45,943 I'm gonna call this one greeterHey. 30 00:01:49,590 --> 00:01:54,590 So this value here now is actually now a function. 31 00:01:54,710 --> 00:01:58,680 Okay. And essentially it is this function. 32 00:01:58,680 --> 00:02:01,410 So what this means is that we can now call 33 00:02:01,410 --> 00:02:05,323 this greeter function just as if it was any other function 34 00:02:05,323 --> 00:02:07,953 that we defined ourselves. 35 00:02:07,953 --> 00:02:10,536 So let's say greeterHey Jonah's 36 00:02:12,200 --> 00:02:14,350 and let's call it another time. 37 00:02:14,350 --> 00:02:18,401 Greeter Hey Steven 38 00:02:18,401 --> 00:02:20,540 and now I'm gonna run it. 39 00:02:20,540 --> 00:02:24,610 And indeed we get Hey Jonas and Hey Steven. 40 00:02:24,610 --> 00:02:28,133 And so this worked again because this greeterHey, 41 00:02:28,133 --> 00:02:30,630 it's essentially this. 42 00:02:30,630 --> 00:02:34,020 And so now we're calling it with the argument of Jonas. 43 00:02:34,020 --> 00:02:36,650 And so this name here is then of course, 44 00:02:36,650 --> 00:02:38,810 this name that we specified here. 45 00:02:38,810 --> 00:02:41,013 Now, the greeting is still coming from 46 00:02:41,013 --> 00:02:43,592 this greet function here. 47 00:02:43,592 --> 00:02:46,483 And in case you're wondering why that actually works, 48 00:02:46,483 --> 00:02:50,760 it is because of something called a closure. 49 00:02:50,760 --> 00:02:54,100 Now closures are a very complex and difficult 50 00:02:54,100 --> 00:02:57,146 to understand mechanism that's part of JavaScript. 51 00:02:57,146 --> 00:03:00,320 And so there are two separate videos at the end 52 00:03:00,320 --> 00:03:02,800 of the section about closures. 53 00:03:02,800 --> 00:03:04,300 So closures is one of the 54 00:03:04,300 --> 00:03:07,870 most misunderstood topics in JavaScript. 55 00:03:07,870 --> 00:03:09,553 So don't worry about that Now, 56 00:03:10,501 --> 00:03:13,430 what matters here is that our first function a greet 57 00:03:13,430 --> 00:03:17,182 returned a new function that we stored into this variable. 58 00:03:17,182 --> 00:03:20,753 And so this variable is now just a function that we can call 59 00:03:20,753 --> 00:03:25,240 as we did here again sing the parenthesis syntax. 60 00:03:25,240 --> 00:03:28,493 And of course we could also do it all in one go. 61 00:03:29,490 --> 00:03:33,642 So we can again, call greet. let's say hello now. 62 00:03:33,642 --> 00:03:38,130 And so again this year is now a function. 63 00:03:38,130 --> 00:03:39,932 Okay so if this is a function, 64 00:03:39,932 --> 00:03:44,860 we can immediately call it, right? And so we call like this, 65 00:03:44,860 --> 00:03:48,410 and then we passed into name which is the argument 66 00:03:48,410 --> 00:03:52,750 of this function here, right? And so even though 67 00:03:52,750 --> 00:03:56,090 this looks a bit weird, it is gonna to work. 68 00:03:56,090 --> 00:04:00,580 And so we get hello Jonas now.All right. 69 00:04:00,580 --> 00:04:04,000 And now this example might look a bit weird 70 00:04:04,000 --> 00:04:07,270 and unnecessary for you Like what's the point 71 00:04:07,270 --> 00:04:10,400 of having functions returning other functions? 72 00:04:10,400 --> 00:04:12,620 Well, this will actually become extremely 73 00:04:12,620 --> 00:04:15,070 useful in some situations. 74 00:04:15,070 --> 00:04:17,650 And especially if we're using a really important 75 00:04:17,650 --> 00:04:20,960 programming paradigm called functional programming. 76 00:04:20,960 --> 00:04:23,510 And I think I've mentioned it sometimes throughout 77 00:04:23,510 --> 00:04:25,360 the course and we're actually gonna 78 00:04:25,360 --> 00:04:29,520 look at functional programming by the end of the course. 79 00:04:29,520 --> 00:04:32,150 Maybe not by the time I first published the course, 80 00:04:32,150 --> 00:04:34,610 but certainly some point later. 81 00:04:34,610 --> 00:04:37,031 Anyway make sure to understand this here 82 00:04:37,031 --> 00:04:40,160 and especially this line of code. 83 00:04:40,160 --> 00:04:42,300 And if you understand this, then I'm sure 84 00:04:42,300 --> 00:04:45,123 you understood everything what happened here. 85 00:04:46,030 --> 00:04:48,730 Now, just as a small challenge to finish here, 86 00:04:48,730 --> 00:04:51,399 try to rewrite this function here 87 00:04:51,399 --> 00:04:53,940 using only arrow functions. 88 00:04:53,940 --> 00:04:57,220 And believe me that's gonna look a little bit confusing, 89 00:04:57,220 --> 00:04:59,060 but I'm sure you can do it. 90 00:04:59,060 --> 00:05:01,770 So just take some time and try to rewrite 91 00:05:01,770 --> 00:05:04,560 that greet function using arrow functions. 92 00:05:04,560 --> 00:05:06,110 And I see you here in a minute. 93 00:05:08,860 --> 00:05:10,320 Okay, 94 00:05:10,320 --> 00:05:11,190 so let's 95 00:05:12,940 --> 00:05:14,170 see how it's done 96 00:05:16,790 --> 00:05:18,220 so greet 97 00:05:18,220 --> 00:05:19,733 Just gonna call it R, 98 00:05:21,770 --> 00:05:24,090 so this one takes again, 99 00:05:24,090 --> 00:05:28,130 greeting as an argument and it returns a new function. 100 00:05:28,130 --> 00:05:30,810 So this means that it only has one line of code, 101 00:05:30,810 --> 00:05:33,030 which returns something. 102 00:05:33,030 --> 00:05:34,700 So all we need is this arrow. 103 00:05:34,700 --> 00:05:37,010 And then we don't even need the curly braces 104 00:05:37,010 --> 00:05:40,050 and we don't need to return a statement. 105 00:05:40,050 --> 00:05:42,490 So what are we gonna return from here? 106 00:05:42,490 --> 00:05:43,970 A new function. 107 00:05:43,970 --> 00:05:48,140 So again, an arrow function and so another arrow here, 108 00:05:48,140 --> 00:05:49,370 and then simply this 109 00:05:53,430 --> 00:05:55,800 let's give it a safe and a try 110 00:05:57,110 --> 00:05:57,970 So greet 111 00:05:58,920 --> 00:05:59,753 R 112 00:06:00,710 --> 00:06:04,860 and let's use hi, this time and yeah, 113 00:06:04,860 --> 00:06:06,133 we get hi Jonas, 114 00:06:07,700 --> 00:06:08,800 okay? 115 00:06:08,800 --> 00:06:10,645 So this is an even shorter way 116 00:06:10,645 --> 00:06:13,850 of writing the same function but in my opinion, 117 00:06:13,850 --> 00:06:16,540 it's actually a lot more confusing. 118 00:06:16,540 --> 00:06:18,250 And that's why I wrote it using 119 00:06:18,250 --> 00:06:20,440 this more traditional way here. 120 00:06:20,440 --> 00:06:21,273 But in the end, 121 00:06:21,273 --> 00:06:24,350 it's also simply one arrow function 122 00:06:24,350 --> 00:06:26,800 returning another arrow function. 123 00:06:26,800 --> 00:06:28,855 And so that's the essence of this video, 124 00:06:28,855 --> 00:06:30,569 which I hope was clear to you. 125 00:06:30,569 --> 00:06:34,163 And if so, then let's move on right to the next one.