Using JavaScript's Built-in Objects

In this column, we'll tell you what <br>they are and how to use them

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

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.

String management methods include substring, indexOf, lastIndexOf, and toLowerCase. These are used to return or change the content of the string in some way. For instance, the substring method returns a specified portion of a string. The indexOf method determines the location of a character or group of characters in a string. And the toLowerCase method converts the string to lower case. (As you can imagine, there's also a toUpperCase method.)

Text format methods are used to format text in a document in some special way, and are provided as alternatives to using HTML tags for the same purpose. These methods include big, small, sup, sub, anchor, link, and blink.

String methods can be used directly on strings, or on variables that contain strings. Methods always use open and closed parentheses, even if the method doesn't use parameters. For instance, to convert text to upper case, you'd use one of the following:

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