介绍host概念
与普通的语言不同的是，JavaScript一开始就被设计为一个嵌入式的语言。这意味着，它是寄生在某个环境中而不是自足的。当然，这也意味着其运行环境的边境就是JavaScript的能力边境。JavaScript所寄居的那个运行环境叫做JavaScript的Host。JavaScript跟Host环境之间可以进行非常方便的交流和沟通，并且，以其寄宿的Host作为自己的世界。JavaScript的Host多种多样，包括Browser，Web Server，Flash player，Photoshop，……以及所有支持以JavaScript为其接口脚本语言的各种环境。这儿，我们的重点就是Brower。
window就是Global
我们知道，JavaScript语言规范本身定义了一系列的对象。这些对象被称作built-in对象，它要求JavaScript无论在任何Host中都拥有，或者说Built-in对象就是一个约定。也就是说，JavaScript期望这些built-in对象在任何Host中都是一致的。当然， Host可以增添一些对象，或者修改一些对象的property，毕竟，我们知道修改JavaScript对象是很方便的。在Browser这个 JavaScript最流行的Host里面，增加了很多Host定义的对象，这些对象全是被一个标准体系规定的，这个体系叫做DOM。下面我会详细的介绍 DOM标准的。不过需要明确指出的是：Browser对于DOM标准总是半遮半掩，也就是说：它们实现了部分的DOM标准，同时又扩展了部分DOM没有规定的东西。
无论如何，我们首先需要明确的是：window就是Global。Global是JavaScript的内建对象，window是 Brower提供的Global对象，不过，名字叫window。实现基本上类似于var window = Global; window.newProperty = content; window.oldProperty = updateContent;……。window也像Global一样，可以省略"window."来直接引用其属性。
附加的对象有哪些？
Brower 向JavaScript中附加的对象是非常多的。而且对于不同的Browser，其附加的对象也各不相同。不过大致都会有window（作为Global 存在，提供一些基本的实用功能），document（作为Brower中展现的文档的入口存在），styleSheet（作为样式单操作入口）， event（作为事件），xmlHttpRequest（作为异步http通信通道）等等。后面我们自然要一一深究这些对象，不过现在我们可以暂且放过它们。
DOM是什么
DOM是Document Object Model的缩写，它是一个标准族。它规定了Browser相关的对象扩展应该有哪些properties，它们各是什么意义和作用等等。由于DOM是一个独立标准，并不依赖于JavaScript（也就是说，它规定了Browser应该提供的对象以及接口，可是这些对象是用JavaScript引用还是用C++引用它并没有规定），所以它是用了语言独立的IDL来描述这些对象的外貌和功用。关于DOM跟JavaScript的关联，他们把它叫做 binding。
再一次明确一下，DOM是一个标准族，它描述了Browser应该提供的对象的接口。
DOM标准族包括哪些？
DOM 标准族包括XML DOM，HTML DOM，CSS DOM……，其中每一个都有可能是好几个相关的部分组成的。其中最为主要的标准系列就是XMLDOM了。我准备把它们的规范用IDL描述出来，在我认为必要的地方加上简短的说明。关于IDL，其实完全是不言自明的，所以我就不介绍IDL的语法了。
注意：我描述的DOM规范，比较新，有很多特性还没有被Browser支持，而且有些可能还会改动，但改动的幅度不会很大。但是我宁愿描述一个新的合理的规范，也不愿意描述一个老的不完全的规范。
现在开始XML DOM的描述，这是整个DOM标准的核心和基础。DOM标准的基本思想是把一个用标签（tag）标记（mark）的文本文档看作一棵树，文本文档中的任何一段文本都属于这个树的某个节点，每个节点都有一个唯一的父结点，都有若干子节点和属性。
下面是XML DOM的core部分，基础中的基础。
valuetype DOMString sequence<unsigned short>
typedef unsigned long long DOMTimeStamp;
typedef any DOMUserData;
typedef Object DOMObject;
interface DOMImplementation;
interface DocumentType;
interface Document;
interface NodeList;
interface NamedNodeMap;
interface UserDataHandler;
interface Element;
interface TypeInfo;
interface DOMLocator;
exception DOMException
unsigned short code;
// ExceptionCode
const unsigned short INDEX_SIZE_ERR = 1;
const unsigned short DOMSTRING_SIZE_ERR = 2;
const unsigned short HIERARCHY_REQUEST_ERR = 3;
const unsigned short WRONG_DOCUMENT_ERR = 4;
const unsigned short INVALID_CHARACTER_ERR = 5;
const unsigned short NO_DATA_ALLOWED_ERR = 6;
const unsigned short NO_MODIFICATION_ALLOWED_ERR = 7;
const unsigned short NOT_FOUND_ERR = 8;
const unsigned short NOT_SUPPORTED_ERR = 9;
const unsigned short INUSE_ATTRIBUTE_ERR = 10;
const unsigned short INVALID_STATE_ERR = 11;
const unsigned short SYNTAX_ERR = 12;
const unsigned short INVALID_MODIFICATION_ERR = 13;
const unsigned short NAMESPACE_ERR = 14;
const unsigned short INVALID_ACCESS_ERR = 15;
const unsigned short VALIDATION_ERR = 16;
const unsigned short TYPE_MISMATCH_ERR = 17;
interface DOMStringList
DOMString item(in unsigned long index);
readonly attribute unsigned long length;
boolean contains(in DOMString str);
interface NameList
DOMString getName(in unsigned long index);
DOMString getNamespaceURI(in unsigned long index);
readonly attribute unsigned long length;
boolean contains(in DOMString str);
boolean containsNS(in DOMString namespaceURI, in DOMString name);
interface DOMImplementationList
DOMImplementation item(in unsigned long index);
readonly attribute unsigned long length;
interface DOMImplementationSource
DOMImplementation getDOMImplementation(in DOMString features);
DOMImplementationList getDOMImplementationList(in DOMString features);
interface DOMImplementation
boolean hasFeature(in DOMString feature, in DOMString version);
DocumentType createDocumentType(in DOMString qualifiedName, in DOMString publicId, in DOMString systemId) raises(DOMException);
Document createDocument(in DOMString namespaceURI, in DOMString qualifiedName, in DocumentType doctype) raises(DOMException);
DOMObject getFeature(in DOMString feature, in DOMString version);
interface Node
// NodeType
const unsigned short ELEMENT_NODE = 1;
const unsigned short ATTRIBUTE_NODE = 2;
const unsigned short TEXT_NODE = 3;
const unsigned short CDATA_SECTION_NODE = 4;
const unsigned short ENTITY_REFERENCE_NODE = 5;
const unsigned short ENTITY_NODE = 6;
const unsigned short PROCESSING_INSTRUCTION_NODE = 7;
const unsigned short COMMENT_NODE = 8;
const unsigned short DOCUMENT_NODE = 9;
const unsigned short DOCUMENT_TYPE_NODE = 10;
const unsigned short DOCUMENT_FRAGMENT_NODE = 11;
const unsigned short NOTATION_NODE = 12;
readonly attribute DOMString nodeName;
attribute DOMString nodeValue;
// raises(DOMException) on setting
// raises(DOMException) on retrieval
readonly attribute unsigned short nodeType;
readonly attribute Node parentNode;
readonly attribute NodeList childNodes;
readonly attribute Node firstChild;
readonly attribute Node lastChild;
readonly attribute Node previousSibling;
readonly attribute Node nextSibling;
readonly attribute NamedNodeMap attributes;
readonly attribute Document ownerDocument;
Node insertBefore(in Node newChild, in Node refChild) raises(DOMException);
Node replaceChild(in Node newChild, in Node oldChild) raises(DOMException);
Node removeChild(in Node oldChild) raises(DOMException);
Node appendChild(in Node newChild) raises(DOMException);
boolean hasChildNodes();
Node cloneNode(in boolean deep);
void normalize();
boolean isSupported(in DOMString feature, in DOMString version);
readonly attribute DOMString namespaceURI;
attribute DOMString prefix;
// raises(DOMException) on setting
readonly attribute DOMString localName;
boolean hasAttributes();
readonly attribute DOMString baseURI;
// DocumentPosition
const unsigned short DOCUMENT_POSITION_DISCONNECTED = 0x01;
const unsigned short DOCUMENT_POSITION_PRECEDING = 0x02;
const unsigned short DOCUMENT_POSITION_FOLLOWING = 0x04;
const unsigned short DOCUMENT_POSITION_CONTAINS = 0x08;
const unsigned short DOCUMENT_POSITION_CONTAINED_BY = 0x10;
const unsigned short DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC = 0x20;
unsigned short compareDocumentPosition(in Node other) raises(DOMException);
attribute DOMString textContent;
// raises(DOMException) on setting
// raises(DOMException) on retrieval
boolean isSameNode(in Node other);
DOMString lookupPrefix(in DOMString namespaceURI);
boolean isDefaultNamespace(in DOMString namespaceURI);
DOMString lookupNamespaceURI(in DOMString prefix);
boolean isEqualNode(in Node arg);
DOMObject getFeature(in DOMString feature, in DOMString version);
DOMUserData setUserData(in DOMString key, in DOMUserData data, in UserDataHandler handler);
DOMUserData getUserData(in DOMString key);
interface NodeList
Node item(in unsigned long index);
readonly attribute unsigned long length;
interface NamedNodeMap
Node getNamedItem(in DOMString name);
Node setNamedItem(in Node arg) raises(DOMException);
Node removeNamedItem(in DOMString name) raises(DOMException);
Node item(in unsigned long index);
readonly attribute unsigned long length;
Node getNamedItemNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
Node setNamedItemNS(in Node arg) raises(DOMException);
Node removeNamedItemNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
interface CharacterData : Node
attribute DOMString data;
// raises(DOMException) on setting
// raises(DOMException) on retrieval
readonly attribute unsigned long length;
DOMString substringData(in unsigned long offset, in unsigned long count) raises(DOMException);
void appendData(in DOMString arg) raises(DOMException);
void insertData(in unsigned long offset, in DOMString arg) raises(DOMException);
void deleteData(in unsigned long offset, in unsigned long count) raises(DOMException);
void replaceData(in unsigned long offset, in unsigned long count, in DOMString arg) raises(DOMException);
interface Attr : Node
readonly attribute DOMString name;
readonly attribute boolean specified;
attribute DOMString value;
// raises(DOMException) on setting
readonly attribute Element ownerElement;
readonly attribute TypeInfo schemaTypeInfo;
readonly attribute boolean isId;
interface Element : Node
readonly attribute DOMString tagName;
DOMString getAttribute(in DOMString name);
void setAttribute(in DOMString name, in DOMString value) raises(DOMException);
void removeAttribute(in DOMString name) raises(DOMException);
Attr getAttributeNode(in DOMString name);
Attr setAttributeNode(in Attr newAttr) raises(DOMException);
Attr removeAttributeNode(in Attr oldAttr) raises(DOMException);
NodeList getElementsByTagName(in DOMString name);
DOMString getAttributeNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
void setAttributeNS(in DOMString namespaceURI, in DOMString qualifiedName, in DOMString value) raises(DOMException);
void removeAttributeNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
Attr getAttributeNodeNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
Attr setAttributeNodeNS(in Attr newAttr) raises(DOMException);
NodeList getElementsByTagNameNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
boolean hasAttribute(in DOMString name);
boolean hasAttributeNS(in DOMString namespaceURI, in DOMString localName) raises(DOMException);
readonly attribute TypeInfo schemaTypeInfo;
void setIdAttribute(in DOMString name, in boolean isId) raises(DOMException);
void setIdAttributeNS(in DOMString namespaceURI, in DOMString localName, in boolean isId) raises(DOMException);
void setIdAttributeNode(in Attr idAttr, in boolean isId) raises(DOMException);
interface Text : CharacterData
Text splitText(in unsigned long offset) raises(DOMException);
readonly attribute boolean isElementContentWhitespace;
readonly attribute DOMString wholeText;
Text replaceWholeText(in DOMString content) raises(DOMException);
interface Comment : CharacterData
interface TypeInfo
readonly attribute DOMString typeName;
readonly attribute DOMString typeNamespace;
// DerivationMethods
const unsigned long DERIVATION_RESTRICTION = 0x00000001;
const unsigned long DERIVATION_EXTENSION = 0x00000002;
const unsigned long DERIVATION_UNION = 0x00000004;
const unsigned long DERIVATION_LIST = 0x00000008;
boolean isDerivedFrom(in DOMString typeNamespaceArg, in DOMString typeNameArg, in unsigned long derivationMethod);
interface UserDataHandler
// OperationType
const unsigned short NODE_CLONED = 1;
const unsigned short NODE_IMPORTED = 2;
const unsigned short NODE_DELETED = 3;
const unsigned short NODE_RENAMED = 4;
const unsigned short NODE_ADOPTED = 5;
void handle(in unsigned short operation, in DOMString key, in DOMUserData data, in Node src, in Node dst);
interface DOMError
// ErrorSeverity
const unsigned short SEVERITY_WARNING = 1;
const unsigned short SEVERITY_ERROR = 2;
const unsigned short SEVERITY_FATAL_ERROR = 3;
readonly attribute unsigned short severity;
readonly attribute DOMString message;
readonly attribute DOMString type;
readonly attribute DOMObject relatedException;
readonly attribute DOMObject relatedData;
readonly attribute DOMLocator location;
interface DOMErrorHandler
boolean handleError(in DOMError error);
interface DOMLocator
readonly attribute long lineNumber;
readonly attribute long columnNumber;
readonly attribute long byteOffset;
readonly attribute long utf16Offset;
readonly attribute Node relatedNode;
readonly attribute DOMString uri;
interface DOMConfiguration
void setParameter(in DOMString name, in DOMUserData value) raises(DOMException);
DOMUserData getParameter(in DOMString name) raises(DOMException);
boolean canSetParameter(in DOMString name, in DOMUserData value);
readonly attribute DOMStringList parameterNames;
interface CDATASection : Text
interface DocumentType : Node
readonly attribute DOMString name;
readonly attribute NamedNodeMap entities;
readonly attribute NamedNodeMap notations;
readonly attribute DOMString publicId;
readonly attribute DOMString systemId;
readonly attribute DOMString internalSubset;
interface Notation : Node
readonly attribute DOMString publicId;
readonly attribute DOMString systemId;
interface Entity : Node
readonly attribute DOMString publicId;
readonly attribute DOMString systemId;
readonly attribute DOMString notationName;
readonly attribute DOMString inputEncoding;
readonly attribute DOMString xmlEncoding;
readonly attribute DOMString xmlVersion;
interface EntityReference : Node
interface ProcessingInstruction : Node
readonly attribute DOMString target;
attribute DOMString data;
// raises(DOMException) on setting
interface DocumentFragment : Node
interface Document : Node
readonly attribute DocumentType doctype;
readonly attribute DOMImplementation implementation;
readonly attribute Element documentElement;
Element createElement(in DOMString tagName) raises(DOMException);
DocumentFragment createDocumentFragment();
Text createTextNode(in DOMString data);
Comment createComment(in DOMString data);
CDATASection createCDATASection(in DOMString data) raises(DOMException);
ProcessingInstruction createProcessingInstruction(in DOMString target, in DOMString data) raises(DOMException);
Attr createAttribute(in DOMString name) raises(DOMException);
EntityReference createEntityReference(in DOMString name) raises(DOMException);
NodeList getElementsByTagName(in DOMString tagname);
Node importNode(in Node importedNode, in boolean deep) raises(DOMException);
Element createElementNS(in DOMString namespaceURI, in DOMString qualifiedName) raises(DOMException);
Attr createAttributeNS(in DOMString namespaceURI, in DOMString qualifiedName) raises(DOMException);
NodeList getElementsByTagNameNS(in DOMString namespaceURI, in DOMString localName);
Element getElementById(in DOMString elementId);
readonly attribute DOMString inputEncoding;
readonly attribute DOMString xmlEncoding;
attribute boolean xmlStandalone;
// raises(DOMException) on setting
attribute DOMString xmlVersion;
// raises(DOMException) on setting
attribute boolean strictErrorChecking;
attribute DOMString documentURI;
Node adoptNode(in Node source) raises(DOMException);
readonly attribute DOMConfiguration domConfig;
void normalizeDocument();
Node renameNode(in Node n, in DOMString namespaceURI, in DOMString qualifiedName) raises(DOMException);
};
上面说了，这是标准中的基础部分，而且，也是标准中最重要的部分，实际上，如果你知道了这些接口（再加上这些标准接口跟JavaScript在Browser这个Host中的对象的binging），你就可以进行几乎所有的Browser端编程了。
