Functions & Abstraction

	A function is a package for an algorithm; once written, it can be use over and over.

The Package

	Functions have a specific syntax
		function <name> ( <parameter list> ) {
		<function definition>
		}
			<name> names are identifiers; start w/letter
			<parameter list> is the input variables, a list separated by commas
			<function definition> is just the program to do the work

A Sample Function

	Compute the Body Mass Index when the inputs are in metric
			function <name> ( <parameter list> ) {
		<function definition>
		}

Writing Functions

	Most programming is done by writing functions, so learning the form is key

Declarations

	A function is declared by writing down the “package” … the function is used when it is called

Summarizing

	Declaration: the function “package,” says what happens when the function runs
	Call: the function use, asks for the computation to be run
			There is only one function declaration
			There can be many calls … functions are reusable
			In JS, functions tend to be grouped together but the calls go where they are needed

Gold Function

	Suppose we compute “weight in Au”
			Worth = (Weight*12)*368.4
			Begin with the form ...

Gold Function

	Suppose we compute “weight in Au”
			Worth = (Weight*12)*368.4

Gold Function

	Suppose we compute “weight in Au”
			Worth = (Weight*12)*368.4

Gold Function

	Suppose we compute “weight in Au”
			Worth = (Weight*12)*368.4

Testing Template

	No one writes perfect programs the first time … smart programmers check
	To test, have a standard page handy

Declare the Function

	Put a function declaration in <script>

Try The Function

Function Features

	Reviewing properties of functions
			Selecting names … don’t use alert()
			Parameter variables … don’t need to be declared, but work like local variables

Function Features (cont.)

			Scope of Reference … refers to where in the program a variable is “known,” i.e. where its value can be referenced and/or assigned

Function Features (cont.)

			Global … declared outside of functions

Function Features (cont.)

			Parameters vs Arguments … parameters are the “formal” variables in the function declaration; arguments are the same thing in the call

Summary

	Functions are packages for algorithms
			They follow a series of rules, that quickly become intuitive
			Functions have both a declaration and a call
			Functions have both parameters (in the declaration) and arguments (in the call)
			Scope refers to the region of a program where a variable is “known”