You use variables as symbolic names for values in your application. You give variables names by which you refer to them and which must conform to certain rules.
A JavaScript identifier, or name, must start with a letter or underscore ("_"); subsequent characters can also be digits (0-9). Because JavaScript is case sensitive, letters include the characters "A" through "Z" (uppercase) and the characters "a" through "z" (lowercase).
Some examples of legal names are Number_hits, temp99, and _name.
You can declare a variable in two ways:
- By simply assigning it a value; for example, x = 42
- With the keyword var; for example, var x = 42
When you set a variable identifier by assignment outside of a function, it is called a global variable, because it is available everywhere in the current document. When you declare a variable within a function, it is called a local variable, because it is available only within the function. Using var is optional, but you need to use it if you want to declare a local variable inside a function that has already been declared as a global variable.
You can access global variables declared in one window or frame from another window or frame by specifying the window or frame name. For example, if a variable called phoneNumber is declared in a FRAMESET document, you can refer to this variable from a child frame as parent.phoneNumber.
