JavaScript Application Cookbook

questions.js—The JavaScript Source File

Let’s continue with questions.js , the JavaScript source file called by administer.html, shown in Example 2.2.

Example 2-2. The Beginning of the questions.js Source Code

     1  function question(answer, support, question, a, b, c, d) {
     2    this.answer = answer;
     3    this.support = support;
     4    this.question = question;
     5    this.a = a;
     6    this.b = b; 
     7    this.c = c;
     8    this.d = d;
     9    return this;
    10    }
    11  var units = new Array(
    12    new question("a", "The others are external objects.", 
    13    "Choose the built-in JavaScript object:",   "Image", "mimeType", 
    14    "Password", "Area"),
    15  // and so on ...
    16    }

This is, of course, an abbreviated version of the file. Array units is much longer (75 elements in all), but this shows you that each element of units is a question object as defined in function question() in lines 1-10.

This application is based on user-defined objects (objects that you and I declare). If the concept of JavaScript objects seems obscure, check Netscape’s documentation at http://developer.netscape.com/docs/manuals/communicator/jsguide4/model.htm. It will help you better understand the JavaScript Object Model. In the meantime, use the next few paragraphs as a crash course.

An object is a set of structured data. Each object can own or have associated with it two types of entities—properties and methods. Properties have something, such as the number 6, the expression a * b, or the string “Jimmy.” Methods do something, such as calculate the circumference ...