阮一峰的IT笔记

IE 5 and later support the Level 1 Core and HTML features well enough to run the examples in this chapter, and they support the key Level 2 CSS features well enough to run most of the examples in Chapter 16. Unfortunately, IE 5, 5.5, and 6 do not support the DOM Level 2 Events module, even though Microsoft participated in the definition of this module and had ample time to implement it for IE 6. IE's lack of support for the standard event model impedes the development of advanced client-side web applications.

Although IE 6 claims (through its hasFeature() method) to support the Core and HTML interfaces of the DOM Level 1 standard, this support is actually incomplete. The most egregious problem, and the one you are most likely to encounter, is a minor but annoying one: IE does not support the node-type constants defined by the Node interface. Recall that each node in a document has a nodeType property that specifies what type of node it is. The DOM specification also says that the Node interface defines constants that represent each defined node type. For example, the constant Node.ELEMENT_NODE represents an Element node. In IE (at least as high as version 6), these constants simply do not exist.

The examples in this chapter have been modified to work around this problem by using integer literals instead of the corresponding symbolic constants. For example, you'll see code like this:

if (n.nodeType == 1 /*Node.ELEMENT_NODE*/)  // Check if n is an Element

It is good programming style to use constants instead of hardcoded integer literals in your code, and if you'd like to do this portably, you can include the following code in your programs to define these constants if they are missing:

if (!window.Node) {
    var Node = {            // If there is no Node object, define one
        ELEMENT_NODE: 1,    // with the following properties and values.
        ATTRIBUTE_NODE: 2,  // Note that these are HTML node types only.
        TEXT_NODE: 3,       // For XML-specific nodes, you need to add
        COMMENT_NODE: 8,    // other constants here.
        DOCUMENT_NODE: 9,
        DOCUMENT_FRAGMENT_NODE: 11
    };
}