Original subtitles

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Let's do the opposite of the last lecture 2

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and create a function that returns a new function. 3

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So I'm gonna write a very simple greet function here, 4

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because this is really just to demonstrate this point here 5

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as easily as possible. 6

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So here we can pass in a greeting like hi 7

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or hello or something like that. 8

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And then all this function will do 9

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is to return a new function. 10

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So as always, 11

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we write return and then simply a new function value. 12

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And this new function that we return 13

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will also have a parameter so it will be able 14

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to receive arguments. Right? 15

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And so what this function here will do, 16

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is it will simply look to the console, 17

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basically the greeting, and then the name of the person 18

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that we passed into this function. 19

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So let's just write this 20

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and it will make sense when we see this in action. 21

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I'm sure it looks a bit weird right now. 22

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And now let's actually use the greet function. 23

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So let's say greet 24

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with hey and so 'hey' is the greeting here. 25

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Now what will be the result of this function call? 26

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Well, it's gonna be this function, right? 27

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And so let's store the result of this function call, 28

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which will be as we just said, that function, 29

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I'm gonna call this one greeterHey. 30

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So this value here now is actually now a function. 31

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Okay. And essentially it is this function. 32

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So what this means is that we can now call 33

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this greeter function just as if it was any other function 34

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that we defined ourselves. 35

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So let's say greeterHey Jonah's 36

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and let's call it another time. 37

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Greeter Hey Steven 38

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and now I'm gonna run it. 39

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And indeed we get Hey Jonas and Hey Steven. 40

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And so this worked again because this greeterHey, 41

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it's essentially this. 42

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And so now we're calling it with the argument of Jonas. 43

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And so this name here is then of course, 44

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this name that we specified here. 45

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Now, the greeting is still coming from 46

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this greet function here. 47

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And in case you're wondering why that actually works, 48

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it is because of something called a closure. 49

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Now closures are a very complex and difficult 50

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to understand mechanism that's part of JavaScript. 51

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And so there are two separate videos at the end 52

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of the section about closures. 53

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So closures is one of the 54

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most misunderstood topics in JavaScript. 55

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So don't worry about that Now, 56

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what matters here is that our first function a greet 57

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returned a new function that we stored into this variable. 58

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And so this variable is now just a function that we can call 59

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as we did here again sing the parenthesis syntax. 60

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And of course we could also do it all in one go. 61

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So we can again, call greet. let's say hello now. 62

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And so again this year is now a function. 63

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Okay so if this is a function, 64

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we can immediately call it, right? And so we call like this, 65

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and then we passed into name which is the argument 66

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of this function here, right? And so even though 67

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this looks a bit weird, it is gonna to work. 68

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And so we get hello Jonas now.All right. 69

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And now this example might look a bit weird 70

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and unnecessary for you Like what's the point 71

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of having functions returning other functions? 72

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Well, this will actually become extremely 73

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useful in some situations. 74

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And especially if we're using a really important 75

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programming paradigm called functional programming. 76

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And I think I've mentioned it sometimes throughout 77

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the course and we're actually gonna 78

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look at functional programming by the end of the course. 79

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Maybe not by the time I first published the course, 80

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but certainly some point later. 81

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Anyway make sure to understand this here 82

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and especially this line of code. 83

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And if you understand this, then I'm sure 84

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you understood everything what happened here. 85

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Now, just as a small challenge to finish here, 86

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try to rewrite this function here 87

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using only arrow functions. 88

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And believe me that's gonna look a little bit confusing, 89

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but I'm sure you can do it. 90

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So just take some time and try to rewrite 91

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that greet function using arrow functions. 92

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And I see you here in a minute. 93

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Okay, 94

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so let's 95

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see how it's done 96

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so greet 97

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Just gonna call it R, 98

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so this one takes again, 99

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greeting as an argument and it returns a new function. 100

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So this means that it only has one line of code, 101

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which returns something. 102

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So all we need is this arrow. 103

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And then we don't even need the curly braces 104

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and we don't need to return a statement. 105

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So what are we gonna return from here? 106

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A new function. 107

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So again, an arrow function and so another arrow here, 108

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and then simply this 109

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let's give it a safe and a try 110

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So greet 111

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R 112

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and let's use hi, this time and yeah, 113

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we get hi Jonas, 114

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okay? 115

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So this is an even shorter way 116

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of writing the same function but in my opinion, 117

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it's actually a lot more confusing. 118

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And that's why I wrote it using 119

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this more traditional way here. 120

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But in the end, 121

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it's also simply one arrow function 122

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returning another arrow function. 123

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And so that's the essence of this video, 124

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which I hope was clear to you. 125

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And if so, then let's move on right to the next one.