JavaScript Object-Oriented Concepts

JavaScript is an object-oriented programming (OOP) language, and provides various objects and methods, as well as the ability to create user-defined methods. To use JavaScript effectively, it is important to understand the following concepts:

Properties

Properties are predefined data-storage locations associated with an object. You can 'get' or 'set' these properties to observe or alter the corresponding attributes of the object. For example, every report element has a visibility property: Table1.visible = false;

Methods

Methods are predefined functions associated with an object. (In general, these functions operate on the object itself.) For example, the CALC object provides a method for obtaining today's date: Text1.text = CALC.today();

Events

Events are predefined actions that are recognized by an object, such as mouse movement or clicking. For example, the onPageBreak handler executes every time a page-break event occurs.

JavaScript Syntax Basics

JavaScript syntax is very similar to that of C++ and Java. It uses the same construct for all loops and has similar syntax for operators. The following is a typical script:

var total = 0;
   for(var i = 1;
 i < Table1.table.length;
 i++) {    total += parseInt(Table1.table[i][1]);
 }
   text = (total / Table1.table.length).toFixed(2); 

The following sections cover the basics of programming with JavaScript.

Comments and Names

JavaScript uses double slashes '//' to start a single line comment, and '/* */' to enclose a multi-line comment.

 // single line comment
 /* multi-line
    comment */ 

The semicolon is used as a statement separator:

 var n = 0;
 k = parseInt(123); 

Variable names can only contain alphanumeric characters plus the underscore character (_). They cannot start with a digit and cannot use reserved JavaScript keywords. All symbols in JavaScript are case-sensitive.

Declaration and Assignment

JavaScript is a weakly-typed language. This means that variables are not assigned a type when they are declared. A variable can be assigned any value, and its type is determined by the value currently assigned. Consequently, a local variable does not need to be declared before it is used.

 var variable_name = "Hello";
 // -- recommended message1 = "Hello";
 // -- without “var” also works var count = 100; 

If a variable is used as a report-level variable, it must be declared using the 'var' keyword.

 // Place declaration in the onLoad handler: 
 var pageTotal = 0; 

After the variable is declared, it can be used everywhere as a shared report instance variable.

Object Types and Scopes

JavaScript is object-based. This means that every value in JavaScript is an object. As with any Object Oriented (OOP) language, properties and methods associated with each object generally need to be invoked by qualifying the names with the object name.

 // the following statements are equivalent
 var name = first_name.concat(last_name);
 name = first_name + last_name; 

As is the case in C++ and Java, if a script is running inside an object scope, it can reference its properties and methods without qualifying the name.

 Text1.text = "Hello"; // in report script
 text = "Hello";       // in Text1 script 

JavaScript also has a global scope which provides common methods. Since every script runs within global scope, these methods do not need to be qualified.

 // parseInt() is a global method
 var num = parseInt(parameter['count']);
 // toFixed() is a number method, so it needs to be qualified
 var int_num = num.toFixed(0);