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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

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Page 6 of 7

The Array object in JavaScript does the same work as the makeArray constructor function. You can use it to create a new array, then provide the data for each element in the usual manner. In Netscape 2.0, the Array object ignores any "length" or number of elements value you pass to it, so if you need to store the number of elements in the array, you must do so explicitly. 

var myArray = new Array();
myArray[0] = 3;
myArray[1] = "item 1";
myArray[2] = "item 2";
myArray[3] = "item 3";

When the array is created, JavaScript merely creates an object for it, but doesn't fill any of the elements with an initial value. JavaScript returns null when you access an element of an array that has not been expressly defined. In the example above myArray[4] returns null, since element[4] is not defined.

In Atlas, the Array object accepts a length parameter, so you don't need to set the length separately. Merely pass the number of elements as a parameter of the Array() constructor; you may then refer to the length using the construct array_name.length. You can remove array elements by defining them with null, but the length property remains constant. You can, however, manually change the length property at any time yourself, simply by defining a new value for array_name.length. As in Netscape 2.0, undefined array elements contain a null value.

Object is a generic object constructor, and is borrowed from Java. However, JavaScript's Object is a much simplified version of the Java Object class. In Java, Object is used as a superclass, but in JavaScript, Object is used as a simplified means of creating new objects without providing an object constructor function. In JavaScript, an object constructor function is called with the new statement, and the function defines any properties or methods of the object. In the following simplified example, the calling statement instantiates a new object named myObject. The makeObject function creates the object, defining one property ("name") to it. 

myObject = new makeObject ("my object");
 
function makeObject(name) {
        this.name = name;
        return (this);
}

The Object constructor saves you the trouble of making a constructor function, and is handy when you don't need or want to define methods and properties of the object when it is created, or when you want to define just one two properties. These following two lines replicate the example above: 

myObject = new Object();
myObject.name = "my object";

You might use the Object constructor as a quick means to create an object. One such example is a , color database, which uses JavaScript as a miniature database. The database can consist of just one or two objects; separate properties of the objects contain the individual data items.

The following script uses JavaScript to built a small database lookup application. The Object constructor creates two objects: an index object and a data object. The index object is really an array with 10 elements; each element contains the name of a Netscape-supported color. The data object mirrors the sequence of the color names, and includes the equivalent hexadecimal value for that color -- the color aliceblue is f0f8ff, for example, and blanchedalmond is ffebcd. Note that the same database can be constructed using Array.

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