1. Abstraction and Functions
Professor Robin Burke

2. Outline Function Definitions Functions Function libraries syntax
return value
multiple parameters
local variables
Function libraries

3. Function definition syntax
function FahrToCelsius (tempInFahr) {
return (5/9) * (tempInFahr – 32); }
declaration
start
function name
parameter names
start of body
function body
end of body

4. Scope With functions Local Global levels of interpretation
what happens inside of a function
Global
what happens outside of the function

5. Renamed example 4 animal cow OldMacVerse sound moo global
document.write (...)
animal
cow
OldMacVerse
sound
moo
OldMacVerse
(critter, noise);
("duck", "quack");
global
"testmac.html"
critter
cow
noise
moo

6. Libraries We can define a group of functions Separate file
usually related
Separate file
.js extension
Load using script tag
<script type="text/javascript" src="random.js" />
Call functions from page

7. Example
random.js
pick4.html
convert.js
ctof2.html
ftok.html

8. Debugging examples

9. Computational problem-solving
Initial conditions
what do we know?
what is the input?
Output
what will the solution look like?
Resources
what pieces already exist?

10. Problem decomposition
Identify steps that will lead to a solution
Decompose each step
into steps small enough that they can be implemented
Multiple stages of decomposition may be necessary

11. Pseudocode Programming language is too specific
requires that you make low-level decisions
Useful to describe steps of computation
Pseudocode
describe computation without actually writing the program

12. Example
A page that convert Fahrenheit to Celcius

13. Decomposition 1 Initial conditions Output Resources
Temp F input by user
Output
appropriate HTML
with Celsius temperature
Resources
conversion formula

14. Decomposition 2 Steps Not quite pseudocode get input
calculate conversion
output HTML
Not quite pseudocode
not operations that Javascript can do
can be decomposed further

15. Decomposition 3 get input calculate conversion output HTML
prompt user for temp in F
calculate conversion
temp in C is 5/9 temp in F - 32
output HTML
write temp F to page
write temp C to page

16. Pseudocode Could be realized in multiple programming languages
prompt user for temp in F
temp in C is 5/9 temp in F - 32
write temp F to page
write temp C to page
Could be realized in multiple programming languages
although only a few can be used as web scripting languages

17. New problem Get height and width from user
Display a table (single cell) of this size
with the dimensions inside

18. Next class
Events
Reading
Ch. 9