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Now that we're getting 2

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more comfortable with JavaScript, 3

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it's time to learn about a more theoretical concept. 4

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And that's the difference 5

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between statements and expressions. 6

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And this is gonna be just a very high level overview, 7

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just so that the future lecturers make more sense. 8

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So essentially, an expression is a piece of code 9

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that produces a value. 10

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For example, three plus four is an expression 11

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because this is gonna produce a value, okay? 12

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So I don't even mean the entire line of code. 13

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What I mean is really just this three plus four. 14

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This is an expression, okay? 15

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And again, because it does produce a value. 16

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The same goes, for example for just any number. 17

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This for example is an expression too, 18

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even though it's just a simple value. 19

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But it's still also an expression, 20

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because again, this itself 21

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will produce a value in JavaScript. 22

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Or we can do this. 23

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So true and false and, 24

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not false. 25

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So all of this here, 26

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is an expression, right? 27

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Because this will in the end, produce some Boolean value. 28

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Now, on the other hand, we have statements. 29

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And the statement is like a bigger piece of code 30

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that is executed 31

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and which does not produce a value on itself. 32

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And we can compare this with normal spoken language. 33

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And so in this example, 34

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a declaration is like a complete sentence 35

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and expressions are like the words 36

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that make up the sentences. 37

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Now, basically we write our whole programs 38

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as a sequence of actions. 39

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And these actions are statements. 40

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So let's take as an example, the, if else, statement. 41

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So let's say, 42

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if 23 is greater than 10, 43

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then, well just do something. 44

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So create a string called, 23 is bigger. 45

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The code itself doesn't really matter here. 46

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So this, if else statement is in fact a statement. 47

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And so that's the reason why I have called it 48

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the if else statement all the time. 49

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And the same is true for the switch statement. 50

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So this statement here 51

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doesn't really produce a value, does it? 52

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All it does is, in this case, 53

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it simply declares is variable called STR. 54

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But that's it. 55

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It performs some actions, 56

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in this case, declaring this variable, 57

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but it doesn't produce a value. 58

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And so in that, it's different from, 59

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for example, having this here, okay? 60

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Now the string itself, again is an expression. 61

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So this is probably a bit confusing, 62

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but that's not a problem, okay? 63

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My goal here is not that you understand 64

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the exact rules of what an expression is 65

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and what a statement is, 66

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because, in fact, it's all a bit fuzzy. 67

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So my main goal with this lecture is really 68

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that you know that statements and expressions exist, 69

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and that expressions produce values, 70

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and that statements are like full sentences 71

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that translate our actions. 72

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So the actions that we want the program to perform, okay? 73

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So really that's all you need to know, 74

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and all you need to basically memorize from this video. 75

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We don't need to go into all the details. 76

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So there's no need to start asking a bunch of questions 77

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about this in the Q and A section, all right? 78

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So this will all make even more sense as we move on. 79

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So I said that this string here is itself an expression. 80

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And then this whole line of code is a statement, 81

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because this again does not produce a value. 82

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And so basically, whenever something ends with a semicolon, 83

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that's then a statement. 84

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It's like a complete sentence, okay? 85

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Now this difference between expressions and statements 86

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is important to know 87

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because JavaScript expects 88

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statements and expressions in different places. 89

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For example, in a template literal, 90

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we can only insert expressions, but not statements. 91

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So let me just very quickly 92

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demonstrate that to you. 93

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So we can say, I am, 94

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and then our placeholder here, basically. 95

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And so in here, we need to put an expression. 96

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So something that produces a value 97

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which can then be put into the string 98

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that we're building here using the template literal. 99

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So let's say, 100

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just to do some calculations here. 101

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So 2037 minus 1991, 102

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years old. 103

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So again, this is an expression here. 104

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And so this one will work. 105

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However, we cannot do this. 106

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For example, we could not insert 107

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this if statement in here. 108

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It wouldn't make any sense at all, okay? 109

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Let's try that. 110

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And so we actually get right away, 111

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unexpected token, if. 112

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And that's because JavaScript knows that this is a statement 113

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and statements don't make sense 114

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where JavaScript expects an expression. 115

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Now, if we had a variable, for example, 116

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then if we used that here, 117

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then this would actually also be an expression. 118

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Because this variable 119

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will essentially just be replaced with this string. 120

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And so this produces a value, 121

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and so of course this is completely acceptable. 122

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Okay, and that's actually all I had to show you 123

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in this video. 124

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Again, my goal was really just to make sure 125

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that you kind of understand 126

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the difference between expressions and declarations 127

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so that moving forward, 128

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we are really both on the same page here.