The JavaScript Object Object

Here's another way to create custom objects, as of Netscape Navigator 3 and Internet Explorer 4: You can base them on the JavaScript Object object explicitly. In fact, all JavaScript objects are based on the Object object now, and that means any object you create with the new operator.

For example, here's how I create a new object, object1 , and add a property to it, value , and then store a number in that property and display the stored value:

(Listing 23-10.html on the web site)

 <HTML>      <HEAD>          <TITLE>              Creating a Custom Object          </TITLE>          <SCRIPT LANGUAGE="JavaScript">              <!--             function creator()              {  var object1 = new Object()   object1.value = 5   document.form1.text1.value = "object1.value = " + object1.value  }              // -->          </SCRIPT>      </HEAD>      <BODY>          <H1>Creating a Custom Object</H1>          <FORM NAME="form1">              <INPUT TYPE="BUTTON" ONCLICK="creator()" VALUE="Click Me!">              <BR>              <INPUT TYPE="TEXT" NAME="text1">          </FORM>      </BODY>  </HTML>

You can see the results in Figure 23.11, where we've created a new object using the JavaScript Object object, added a property to it, stored a value in that property, and displayed the stored value.

Figure 23.11. Creating a new object using the JavaScript `Object` object.

graphics/23fig11.gif

You can find the properties and methods of the Object object in Table 23.1 in overview, its properties in depth in Table 23.2, and its methods in Table 23.3 in depth.

Table 23.1. Overview of the Properties and Methods of the Object Object

Properties	Methods
`constructor`	`hasOwnProperty`
`propertyIsEnumerable`	`isPrototypeOf`
`prototype`	`toLocaleString`
	`toString`
	`valueOf`

Table 23.2. The Properties of the Object Object

Property	NS2	NS3	NS4	NS6	IE4	IE5	IE5.5	IE6
`constructor`		x	x	x	x	x	x	x
	Read/write
	This property specifies the function that creates an object.
`propertyIsEnumerable`				x			x	x
	Read/write
	You use this property like this: `object` `.propertyIsEnumerable` `(` `property` `)` . (It looks more like a method, but Microsoft calls it a property.) This property is true if `property` exists in `object` and can be looped over using a `for...in` loop, and false otherwise .
`prototype`		x	x	x	x	x	x	x
	Read/write
	This property returns a reference to the object's prototype. You use the `prototype` property to provide base functionality to a set of objects. See "Adding Methods to Existing Objects" in this chapter for more information.

Table 23.3. The Methods of the Object Object

Method	NS2	NS6	IE5.5	IE6
`hasOwnProperty`		x	x	x
	Returns: Boolean
	This method returns true if an object has a property of the specified name, false if it does not. Syntax: `object.hasOwnProperty(` `name` `)` , where `name` is the name of the property you're checking.
`isPrototypeOf`		x	x	x
	Returns: Boolean
	This method returns true if an object has the current object in its prototype set.
	Syntax: `object.isPrototypeOf(` `name` `)` , where `name` is the name of the object you're checking.
`toLocaleString`		x	x	x
	Returns: String
	Returns an object's data converted to a string using the current locale.
	Syntax: `object` `.toLocaleString()` .
`toString`		x	x	x
	Returns: String
	Returns an object's data converted to a string.
	Syntax: `object` `.toString()` .
`valueOf`		x	x	x
	Returns: Object
	Returns an object's data.
	Syntax: `object` `.valueOf()` .

The JavaScript Object Object