1. JavaScript Functions

2. Storing Information in a Computer

3. Holding information Computer doesn’t understand values
It knows about locations: “cubby holes”
Takes locations and does what you tell it: read, write, add

4. Assignment Statement A = B + C; Cubby Hole 2: add this value
Cubby Hole 3: place it here
A = B + C;
Cubby Hole 1: take this value

5. CUBBY HOLES Types of cubby holes Differences Fields in a form
Specifically defined ones: VARIABLES
Information that you pass around
Differences
Some you can only read
Some you can only write
Some you can do both

6. Changing Information A = A + C; Cubby Hole 2: add this value
Cubby Hole 1: replace the old value
A = A + C;
Cubby Hole 1: take this value

7. Functions

8. What is a function?
Collection of statements that can be invoked as a unit

9. Different Types of Functions
Who writes?
JavaScript provides (alert)
Someone else writes and you use
You write
Do they need to be given information?
Alert does…tell it what to write
Asking for the current date doesn’t
Are they a statement or part of an expression?
Alert is a statement; doesn’t give you anything back
If you ask for the current time, you expect to get something back

10. TODAY JavaScript provides Do they need to be given information?
Both
Are they a statement or part of an expression?

11. Output
Black Box
Inputs

12. Return
Parameters
Function

13. Functions as Statements
Performs an action but doesn’t give you anything back
Example: alert

14. Parameters Call a function with a different value every time
MUST give it everything that it expects
For alert
One parameter, the string to print

15. Alert
String to print
Function

16. But What if I Want a Value Back?
For Assignment 7:
eval(string)
Like alert, takes a string as a parameter
Does its magic on the string
And gives you back a number
You can do what you want with the number
Put it in an alert
Write it out to a form
Do more math on it

17. Using eval formname.fieldname.value = eval(‘3+5’);
alert(eval(formname.inputfield.value));

18. Format of a Function functionName(parm,parm);
Always needs () even if no parameter
functionName();

19. The rules The order of the parameters matter Only a single output
5 - 3 different than 3 -5
Any number of parameters can be defined
Fixed for any specific function
Only a single output
Optional in general
But always the same for any specific function

20. Random Numbers

21. Why random numbers? Variability Different results Examples
Display one of ten pictures
Display one of five quotations
Play a game of chance
All built on a random number!

22. Can computers really create random numbers?
Computers do as they are told
So how can they do something random?
They can’t!
But we can tell them to find a number that changes often!
Needs to not have an easily recognized pattern
Pseudo-random Number Generator
Options?
Time!

23. Getting a random number
Math.random()
Returns a value between 0 and 1
One of a series of mathematical functions
members of a collection called Math
each are prefixed by “Math.”

24. What if you don’t want 0-1? Change range? Multiply Not start at 0? Add
Integers only?
Round
Floor
Ceiling