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Using JavaScript's built-in objects

How to use JavaScript's built-in objects Date, Math, String, Array, and Object

By Gordon Mccomb, JavaWorld.com, 05/01/96

JavaScript sports a number of built-in objects that extend the flexibility of the language. These objects are Date, Math, String, Array, and Object. Several of these objects are "borrowed" from the Java language specification, but JavaScript's implementation of them is different. If you're familiar with Java, you'll want to carefully examine JavaScript's built-in object types to avoid any confusion.

The JavaScript object model is a simple one. The bulk of these objects deal with window content -- documents, links, forms, and so forth. In addition to window-content objects, JavaScript supports a small handful of "built-in" objects. These built-in objects are available regardless of window content and operate independently of whatever page your browser has loaded.

The built-in objects are Date, Math, String, Array, and Object. Each is used in a unique and not-quite-consistent way. Furthermore, newer versions of JavaScript (as found in Netscape "Atlas," currently in beta) implement several of these objects in a different manner than in Netscape 2.0. In this column we will address these built-in objects and how to use them. And we'll make note of the quirks you'll encounter as you apply these objects to your JavaScript pages.

Understanding the string object

Of all JavaScript's objects, the String object is the most commonly used. In the Netscape 2.0 JavaScript implementation, new string objects are created implicitly using a variable assignment. For example,

var myString = "This is a string";

creates a string, with the specified text, called myString. In Netscape 2.0, there is no actual object called string, and attempting to instantiate a new String object using the new statement results in an error, as String (or string) is not a defined keyword. In the Atlas version of Netscape, however, String is a bona fide object, and the String keyword can be used to create new strings. The following two approaches are allowed in Atlas, but not in Netscape 2.0.

var myString = new String();
myString = "This is a string";

and

var myString = new String ("This is a string");

String objects have one property: length. The length property returns the length of the string and uses the syntax string.length, where string is the name of the string variable. Both of the following display 16.

alert ("This is a string".length)

and

var myString = "This is a string";
alert (myString.length);

While there may be just one string property, JavaScript supports a large number of methods that can be used with strings. These methods can be roughly divided into two broad camps: string management and text format.