Original subtitles

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So, I did the math, 2

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and since the beginning of the course, 3

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we have studied, exactly 23 different array methods. 4

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And that's really amazing. 5

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And not just because, 6

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23 is my favorite number, 7

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but because that means, 8

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that you cannot do everything you can imagine, with arrays. 9

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Now, the problem is that, 10

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choosing between 23 different methods, 11

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is not always easy. 12

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And especially when you just started learning about them. 13

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Right? 14

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So probably, in your mind right now, 15

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there is a big confusion, 16

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between all these methods, 17

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and about which one to use, when. 18

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So, to help you out with that, 19

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I created this summary lecture, 20

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with all the 23 array methods. 21

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And I believe, that the best way to figure out, 22

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which method to use, 23

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in each situation, 24

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is by starting to ask the question, 25

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what do I actually want from this method? 26

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So do I want to mutate the original array, 27

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or do I want a new array? 28

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Do I maybe want an array index, 29

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or do I want to retrieve an entire array element? 30

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Or do I want to know, 31

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if an array includes, a certain element, 32

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or maybe I just want to get a new string, 33

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to transform the array to a new value, 34

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or simply to loop over the array? 35

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Well, these are a lot of different scenarios, 36

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and by asking exactly these questions, 37

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we can now categorize the methods, 38

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and then easily choose between them. 39

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So this is kind of a framework, that I developed, 40

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and so let me go briefly, 41

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through all of these different scenarios with you. 42

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So these are the methods that mutate the original array. 43

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So if we want to add an element, 44

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to the original array, 45

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we can use push or unshift. 46

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So we already talked about all of these methods, 47

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so of course I will not explain them again, 48

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this is just a reference for you to keep. 49

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Now anyway, if we want to remove, 50

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from the original, 51

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then we use either, 52

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pop, shift or splice. 53

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And finally, we also talked about, 54

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three other methods that mutate the original array, 55

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which is the reverse, sort and fill methods. 56

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Okay. 57

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So keep in mind, that you have to be careful, 58

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because they do change the underlying array, 59

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that we're working with. 60

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And that many times is not what we want. 61

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So if instead, we want a new array, 62

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then we can use one of these methods. 63

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So if we want to calculate one array, 64

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from the original, then we use map methods. 65

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And this one we use all the time, 66

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as it loops over the original array, 67

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and creates a new one, based on that. 68

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We can also create new arrays, 69

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by filtering for a condition, 70

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or by taking a slice of the original array. 71

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We can also concatenate two arrays, 72

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and create a new array based on that, 73

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and finally, we can flatten the original array, 74

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using flat and flatMap. 75

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Next, sometimes we need an array index. 76

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And for that, 77

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we have the indexOf and findIndex methods. 78

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Now the difference between them, 79

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is that findIndex can basically search, 80

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for an element in the array, 81

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based on a test condition, 82

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that we provide, in the callback function. 83

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But besides that, 84

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they are pretty similar, 85

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and both give us the index, 86

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of a certain element in an array. 87

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Now, if we actually need the array element itself, 88

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then we use, the find method. 89

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And so this one again, 90

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is based on a test condition, 91

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specified in a callback function. 92

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Next up, sometimes it's very important to know, 93

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whether an array includes, 94

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a certain element or not. 95

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And for that we have, 96

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includes, some and every. 97

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So with includes, 98

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we can simply test, 99

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if an array contains a single value, 100

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while on the other hand, 101

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with some and every, 102

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we can specify a condition, 103

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based on a callback function. 104

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So some is gonna return, 105

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if at least one of the elements in the array, 106

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satisfies the condition, 107

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and every, only returns true, 108

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if all of the elements, 109

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satisfy the condition. 110

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So these three methods, 111

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are all return Boolean values, 112

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which is very helpful, 113

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in a condition. 114

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For example, in an if/else statement. 115

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Okay. So that's where you many times will use, 116

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one of these methods. 117

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Next up, sometimes we want to transform an array, 118

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into a string. 119

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And then we use the join method. 120

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Or we might want to reduce the entire array, 121

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to just one value. 122

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And as we already know, 123

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for that, we use the reduce method, 124

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just as we studied in this section. 125

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So in the reduce method, we use an accumulator, 126

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which has like a snowball, 127

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to boil down, an entire array, 128

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to just one single value. 129

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And that value can be of any type. 130

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So it can be a number, string, Boolean, 131

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or even an array or an object. 132

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All right? 133

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And so in fact, we could, 134

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replace some of these methods that we have here, 135

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with a reduce. 136

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Now, if all we want to do, 137

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is to just loop over an array, 138

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without producing any new value, 139

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we use the, forEach method. 140

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So remember, this one does not create a new array, 141

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and in fact, it doesn't create any new value. 142

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All we do in the forEach method is to, 143

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basically just do some work, 144

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but not produce a new value. 145

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All right? And that's it. 146

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That's an overview of all the 23 methods, 147

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that we can use on arrays. 148

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And it might be a good idea, 149

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to somehow keep this overview handy. 150

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For example, print it out on a paper, 151

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or just store it somewhere, on your computer. 152

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Anyway, now all there's left to do in the section, 153

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is to complete the final coding challenge. 154

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So let's do that right in the next video.