0
1
00:00:00,690 --> 00:00:07,590
All right. So we know that the formula is weight in kilograms divided by height squared, and we have to
1

2
00:00:07,590 --> 00:00:09,660
make this line of code work.
2

3
00:00:09,690 --> 00:00:12,260
So let's first try it out in the calculator.
3

4
00:00:12,480 --> 00:00:17,150
Let's say that we first try to square our height which is 1.8 meters.
4

5
00:00:17,160 --> 00:00:21,920
So on a calculator we can simply write 1.8 times 1.8.
5

6
00:00:22,200 --> 00:00:25,420
So 1.8 squared is equal to 3.24.
6

7
00:00:25,530 --> 00:00:30,540
So now we can divide 65 by 3.24. 65
7

8
00:00:30,540 --> 00:00:37,290
divide by 3.24 and we get 20.0617 something something something.
8

9
00:00:37,290 --> 00:00:43,230
All right. So now that we know that this is how we would calculate it on a calculator, then we can simply
9

10
00:00:43,230 --> 00:00:50,100
copy all of this starting code, and open up our Chrome Developer Tools, and paste it into our Snippets
10

11
00:00:50,100 --> 00:00:50,640
tool.
11

12
00:00:50,640 --> 00:00:53,860
So now, we're going to create our function below this line.
12

13
00:00:54,120 --> 00:00:58,520
And the first step to creating any sort of function is the function keyword,
13

14
00:00:58,530 --> 00:01:05,290
right? Then we're going to give our function a name, which we said has to be the name bmiCalculator,
14

15
00:01:05,370 --> 00:01:07,350
so we're going to use that name.
15

16
00:01:07,380 --> 00:01:13,430
Next step is some parentheses, and whether we're going to add some inputs in here.
16

17
00:01:13,440 --> 00:01:19,140
So in this case we're saying that put the input weight first and then put the input height.
17

18
00:01:19,200 --> 00:01:23,660
So our inputs are going to be weight and height.
18

19
00:01:23,670 --> 00:01:29,960
Now we get to open up our curly braces and specify everything that this function is going to do.
19

20
00:01:31,970 --> 00:01:36,090
So this function has to calculate the value of bmi.
20

21
00:01:36,290 --> 00:01:40,670
Remember that the formula is the weight divided by height squared.
21

22
00:01:40,670 --> 00:01:50,230
So bmi is going to equal to the weight input divided by the height input multiplied by itself.
22

23
00:01:50,570 --> 00:01:56,990
And remember, in the previous lesson we talked about Javascrpit numbers, that in order to specify the
23

24
00:01:57,080 --> 00:02:03,500
order of your calculations then you can use the parentheses to set precedence.
24

25
00:02:03,500 --> 00:02:10,100
So by putting those two parentheses there then we say that calculate height times height first and then
25

26
00:02:10,100 --> 00:02:12,790
divide weight by that value.
26

27
00:02:13,160 --> 00:02:21,530
So now in order to get value bmi out of this function, we have to use the return keyword, and we can say
27

28
00:02:21,530 --> 00:02:23,410
return bmi.
28

29
00:02:23,780 --> 00:02:31,220
So now, if we take all of this code and we go back to our exercise here, we paste it in here, and now if
29

30
00:02:31,220 --> 00:02:35,150
I hit Check solution, then you can see that it will pass.
30

31
00:02:35,150 --> 00:02:39,310
Now there's a number of different ways of writing this function.
31

32
00:02:39,350 --> 00:02:41,120
Some of you might have wondered,
32

33
00:02:41,360 --> 00:02:45,460
I don't really want to multiply the height by height in order to get it squared.
33

34
00:02:45,500 --> 00:02:48,810
Why can’t I just raise height to the power of 2?
34

35
00:02:49,040 --> 00:02:51,300
How would I do that in Javascript?
35

36
00:02:51,350 --> 00:02:56,970
Well, as with any query regarding programming, the solution is only a quick google away.
36

37
00:02:57,080 --> 00:03:03,290
So if we search for ‘raise a number to a power’ and we add the keyword Javascript, then you can see that the
37

38
00:03:03,290 --> 00:03:10,330
MDN docs come up with the Math.pow function, and it shows us how to use it.
38

39
00:03:10,360 --> 00:03:12,460
It says that we can simply say Math.
39

40
00:03:12,490 --> 00:03:13,330
pow,
40

41
00:03:13,630 --> 00:03:18,550
and the first number is the base and the second number is the exponent.
41

42
00:03:18,620 --> 00:03:24,110
So this is your squared which will be 2 or cubed which will be 3.
42

43
00:03:24,350 --> 00:03:26,570
And this is how you would use it.
43

44
00:03:26,570 --> 00:03:27,680
So let's try it out
44

45
00:03:27,680 --> 00:03:30,710
in our case. Instead of writing height times height,
45

46
00:03:30,950 --> 00:03:32,490
what if we did Math.
46

47
00:03:32,520 --> 00:03:40,660
pow, set of parentheses, and then we said height, 2, so height to the power of 2?
47

48
00:03:41,030 --> 00:03:47,240
Now, if we check our solution, you can see that our function is still working exactly as we expect it
48

49
00:03:47,240 --> 00:03:47,630
to,
49

50
00:03:47,780 --> 00:03:50,230
but it's now perhaps a little bit more elegant.
50

51
00:03:50,420 --> 00:03:56,840
Now, if you run this code as it is right now, for example we're calculating the BMI from 65 kilograms
51

52
00:03:56,870 --> 00:04:01,040
and 1.8, and then we're logging that BMI into the console,
52

53
00:04:01,190 --> 00:04:03,480
then you can see that we're getting a really long number,
53

54
00:04:03,500 --> 00:04:08,660
20.0672839 etc..
54

55
00:04:08,870 --> 00:04:11,820
Now usually with BMI we're working with whole numbers.
55

56
00:04:11,870 --> 00:04:18,230
So how can we turn this long number with loads of decimal places to simply a whole number?
56

57
00:04:18,230 --> 00:04:20,070
Well again Google is your friend.
57

58
00:04:20,270 --> 00:04:26,720
And if you search for ‘Javascript round a number to the nearest whole number’ or something around there, then
58

59
00:04:26,780 --> 00:04:33,320
the first result that you get is from W3 Schools, and it tells you about the round method, which you can
59

60
00:04:33,320 --> 00:04:41,090
use by saying Math.round, and is similar to the floor method, which simply rounded down your decimal
60

61
00:04:41,090 --> 00:04:41,630
place.
61

62
00:04:41,630 --> 00:04:44,500
But Math.round is more mathematically correct.
62

63
00:04:44,690 --> 00:04:48,380
So if it's 2.5 it will round it to 3, and if it's 2.4
63

64
00:04:48,420 --> 00:04:49,690
it’ll round it to 2.
64

65
00:04:49,940 --> 00:04:52,950
So let's try using this in our solution.
65

66
00:04:53,000 --> 00:05:03,050
So if, instead of returning bmi, we returned Math.round, and inside the parentheses we enclosed our
66

67
00:05:03,050 --> 00:05:06,190
bmi, as a number with decimal places.
67

68
00:05:06,200 --> 00:05:12,460
Now if we run our code you can see that we only get 20 back which is exactly what we wanted.
68

69
00:05:12,680 --> 00:05:20,400
And if you change our solution to this updated one inside our testing suite, then you can see that our solution
69

70
00:05:20,560 --> 00:05:21,880
also passes.
70

71
00:05:22,100 --> 00:05:26,600
So I hope that was interesting and we've got a few more of these challenges coming up for you.
71

72
00:05:26,750 --> 00:05:27,990
So keep your eyes peeled.
72

73
00:05:28,040 --> 00:05:32,630
But in the next lesson, we're going to dive deeper into Javascript, and we're going to learn all about
73

74
00:05:32,630 --> 00:05:33,770
control flow.
74

75
00:05:34,040 --> 00:05:36,990
So you have all of that and more to look forward to.
75

76
00:05:37,100 --> 00:05:38,600
So I'll see you on the next module.