Basic JavaScript knowledge

There are many types of JavaScript variables.

When you assign a text value to a variable, enclose the value in double or single quotation marks.

Do not use quotation marks when the value you assign to a variable is numeric. If you enclose a value in quotation marks, the value is treated as text.

JavaScript is sensitive to capitalization.

JavaScript does not use a value to declare a variable whose value is actually undefined.

After the following statement has been executed, the value of the variable carname will be undefined:

var carname;

If you re-declare a JavaScript variable, the value of the variable is not lost:

After the following two statements are executed, the value of the variable carname remains "Volvo":

var carname= "Volvo";
var carname;

JavaScript Boolean (logic) can have only two values: TRUE or FALSE.

The following code creates an array named cars:

var cars=new Array ();
Cars[0]= "Audi";
Cars[1]= "BMW";
Cars[2]= "Volvo";

or (condensed array):

var cars=new Array ("Audi", "BMW", "Volvo");

or (literal array):

var cars=["Audi", "BMW", "Volvo";

JavaScript objects

Objects are separated by curly braces. Inside the parentheses, the properties of the object are defined in the form of name and value pairs (name:value). Attributes are separated by commas:

var person={firstname: "Bill", LastName: "Gates", id:5566};

The object (person) in the example above has three attributes: FirstName, LastName, and ID.

Object properties are addressed in two ways:

name=person.lastname;name=person["LastName"];

Undefined and Null

Undefined This value indicates that the variable does not contain a value.

You can empty a variable by setting the value of the variable to null.

Basic JavaScript knowledge