JavaScript Objects

Dateline: 10/05/99

Many programming languages are what we call "Object Oriented."  This means that you can create your own custom groupings of functions and data in a way that makes sense to your programming approach.

To illustrate what I'm talking about, you could create define a type of object (often called a "class") for an employee of a company.  This definition might include variables for salary, time with the company, job title, social security number, etc.  You may also want to define some functions that apply to an employee; maybe a function to write a paycheck, promote the employee, or whatever.

If you've used object oriented languages like C++ or Java, you're probably following me here without difficulty.  If not, read on: everything will become clear.

JavaScript isn't exactly Object Oriented like C++ or Java.  JavaScript is referred to as "Object-Based."  This means that you can't define object types quite like you would in an object oriented language, but you can still take advantage of most of the object functionality.

To define an object type in JavaScript, you must define it as a function.  You can use the "this" keyword to assign variables and initial values (for the programming savvy, this is like using constructors in object oriented languages).

function Employee()
{
 this.Salary = 0;
 this.TimeEmployed = 0;
 this.JobTitle = "";
 this.SocialSecurity = "";
}

To create this object (called an "instance" of the object), use the "new" keyword.

var John = new Employee();

Now you can work with the values of each employee separately.

John.Salary = 100000;
John.TimeEmployed = 10;
John.JobTitle = "CEO";
John.SocialSecurity = "123-45-6789";

var Mary = new Employee();
Mary.Salary = 75000;
Mary.TimeEmployed = 5;
Mary.JobTitle = "JavaScript Programmer";
Mary.SocialSecurity = "987-65-4321"

To see a brief example of JavaScript objects in action, visit my Very Simple Airline Reservation System.

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