Variables

All variables are declared with the 'var' keyword
Variables do not have an explicit data type. There are 3 primitive data types.
Variables do not have a data type until a value is assigned to it and at that point the correct data type is inferred.
The semi-colon is optional when statements are followed by a line break.

var myNumber1 = 10;        // number data type 
var myNumber2 = 5.38;      // number data type 
var myString = "text";     // string data type 
var myBoolean = false;     // boolean data type 

var varData = data; 
var varName = "Smith"; 
var varAge = 26; 
var isOdd = false; 

All On One Line

The semi-colon is required when you have two or more statements on the same line.
This line creates 3 variables and assigns them values

var myObject = new Object(), myString = 'sometext', myNumber = math.random();  

Global scope

If the var keyword is omitted and a value is just assigned to a variable then it will have 'global scope'.
For global scope just leave off the var

varData = "smith";