JavaScript Lecture4          

Instructor: Amadou O. Wane
Last update: 09/24/01

Lecture4

Variable Scope
A variable that is defined outside of a function is a global variable. A variable that is defined inside of a function is a local variable. What does this mean? Global variables can be used anywhere in the document that is currently loaded in the browser. They can be declared in the HEAD section and used in any function or even in the BODY section. Local variables can only be used in the function that declares them. 

//Varible scope
//Local scope vs. global scope
var g = 99;//Global variable
function my_addition(a,b)
{ var l = a + b; //Local variable
document.write("The c variable is:" + l);
document.write("<br>The g variable is:" + g);
}

my_addition(10,20);
//-----------------------------------------------
If Statement
The if statement is one of the most used features of JavaScript. It is basically the same in JavaScript as it is in other programming languages. If you are new to programming, you should spend some time understanding how the if statement works. You use the if statement in JavaScript to make decisions. The syntax for it is as follows:

 if (condition){
   statements
   }

//If Statements
/*if (condition)
{	statements
}
else
{	statements
}*/
var my_age = 99;
if (my_age >= 18)
{	document.write("<br>You are an adult");
}
The if keyword identifies this as an if statement. The condition in the parenthesis ( ) is evaluated to determine if true, and if so then the statements inside the curly braces { } are executed, otherwise they are skipped and the programs continues with the first line after the if statement.

An optional else statement can be included with the if statement as follows:

 if (condition){
   statements
   }
 else{
   statements
   }   

In this case, the statements inside of curly brackets { } after the else keyword are executed if the condition of the if statement is false.

Switch Statement
var d = new Date()
theDay=d.getDay()
switch (theDay)
{
case 5:
document.write("Finally Friday")
break
case 6:
document.write("Super Saturday")
break
case 0:
document.write("Sleepy Sunday")
break
default:
document.write("I'm really looking forward to this weekend!")
}

var myColor = "unknown";
var hexColor = "FF0000";
switch(hexColor)
{ case
var myColor = "Red";

}