DOM : Document Object Model
 
D is for document : 
The DOM cant work without a document . When you create a web page and load it in a web browser, the DOM comes to life. It takes the document that you have written and turns it into 
an object .
 
O is for Objects : Just as we see before. 
 
M is for Model :
The M in DOM stands for Model, but it could just as easily stand for Map.
The DOM represents the web page thats currently loaded in the browser window. The browser 
provides a map (or a model) of the page. You can use JavaScript to read this map.
 
The most important convention used by the DOM is the representation of a document as a tree.
More specifically, the document is represented as a family tree.

However, instead of using the term family tree, its more accurate to call a document a node tree.
 
 
Nodes :
A document is a collection of nodes, with nodes as the branches and leaves on the document tree.
There are a number of defferent types of nodes. Lets take a quick look at three of them :
element nodes, text nodes, attribute nodes.
 
Element nodes :
such as <body> <p> <ul> , Elemnets are the basic building blocks of documents on the Web, and 
its the arrangement of these elements in a document that gives the document its structure.
 
Text nodes: 
if a document consisted purely of empty elements, it would have a structure, but the document 
itself wouldnt contain much content. On the web, most content is provided by text.
such as <p>Dont forget to buy this stuff</p> , "Dont forget to buy this stuff" is a text node.
In XHTML, text nodes are always enclosed within element nodes.
 
Attribute nodes:
Attributes are used to give more specific information about an element. 
<p title = "a gentle reminder"> Dont forget to buy this stuff. </p>
In DOM, title = "a gentle reminder" is an attribute node.

Because attributes are always placed within opening tags, attribute nodes are always contained 
within element nodes. Not all elements contain attribute, but all attributes are contained by elements.
 
In fact, each element in a document is an object. Using the DOM, you can "get" at all of these 
elements .
 
 
Getting Elements :
 
Three DOM methods allow you to access element nodes by ID, tag name, and class name.
 
getElementById() :
usage : document.getElementById(id) :
this method will return a specific object in the document model.
you can use the typeof to test this : eg :     
        alert( typeof document.getElementById("purchases") ) ;
 
getElementsByTagName() :
usage :   element.getElementByTagName( tag );
Even if there is only one element with the specified tag name, getElementByTagName still returns 
an array. The length of the array will be simply 1.
you can also use a wildcard(通配符) with getElementByTagName, which means you can make an 
array with every single element. eg :
        alert ( document.getElementsByTagName("*").length ) ; 
you can also combine getElementsByTagName with getElementById. eg :
        var shopping = document.getElementById("purchases") ;
        var items = shopping.getElementsByTagName("*") ;
        alert( items.length ); 
 
getElementsByClassName() 
It also behaves in the same way as getElementsByTagName by returning an array of elements with a common class name.The getElementsByClassName method is quite useful, but it’s supported by only modern browsers. To make up for this lack of support, DOM scripters have needed to roll their own getElementsByClassName function using existing DOM methods, sort of like a rite of passage.
function getElementsByClassName(node, classname) {

    if (node.getElementsByClassName) {

        // Use the existing method

        return node.getElementsByClassName(classname);

     } else {

        var results = new Array();

        var elems = node.getElementsByTagName("*");

            for (var i=0; i<elems.length; i++) {

                if (elems[i].className.indexOf(classname) != -1) {

                　　results[results.length] = elems[i];

             　　}

    　　　　 }

        return results;

    }

}
Before you may write like this : 
        var shopping = document.getElementById("purchases");
        var sales = shopping.getElementsByClassName("sale");
With this function, you can write the code like this :
         var shopping = document.getElementById("purchases");
         var sales = getElementsByClassName(shopping, "sale");
 
 
Here's a quick summary of what you've seen so far :
  1. A document is a tree of nodes.
  2. There are different types of nodes : elements, attributes, text, and so on
  3. you can go straight to a specific element node using getElementById.
  4. you can go directly to a collection of element nodes using getElementsByTagName or getElementsByClassName
  5. Every one of these nodes is an object.
 
Getting and Setting Attributes : 
getAttribute()
usage :  object.getAttribute( attribute ) ;
Unlike the other methods you've seen before, you cant use getAttribute on the document object.
It can be used on only an element node object. 
 
SetAttribute()
usage :   object.setAttribute(attribute, value);

The DOM in JavaScript的更多相关文章

  1. HTML与DOM BOM javascript

    1.什么是DOM? 简单说就是DOM规定了HTML,XML等的一些文档映射规范,使JavaScript可以根据这些规范来进行获取元素,在元素上进行各种操作,使得用户页面可以动态的变化,从而大大使页面的 ...

  2. 第61节:Java中的DOM和Javascript技术

    Java中的DOM和Javascript技术 DOM是一门技术,是文档对象模型.所需的文档只有标记型文档,如我们所学的html文档(文档中的所有标签都封装成为对象了) DOM: 为Document O ...

  3. DOM与JavaScript、jQuery之间的关系

    DOM(document object model) 其实是浏览器内元素对象的一个总称 我们用JavaScript对网页进行的所有操作都是通过DOM进行的.DOM属于浏览器,而不是JavaScript ...

  4. javascript+dom 做javascript图片库

    废话不多说 直接贴代码 <!DOCTYPE html><html lang="en"><head> <meta charset=" ...

  5. DOM（JavaScript高程笔记）

    一.节点层次 1.Node类型 if (someNode.nodeType == 1){ // 适用于所有浏览器 alert("Node is an element."); } N ...

  6. html dom与javascript的关系 -我们用JavaScript对网页（HTML）进行的所有操作都是通过DOM进行的

    一,什么是DOM (参考源http://www.cnblogs.com/chaogex/p/3959723.html) DOM是什么 DOM全称为The Document Object Model,应 ...

  7. HTML(DOM)与JavaScript嵌套数组之间相互转换

    html2ja:将html目标元素解析为JavaScript数组字面量,每项的值为tagName, className, id等CSS选择器组合: showJa:将html2ja生成的数组缩进格式化显 ...

  8. DOM，javascript，Web API之间的关系——onclick 引起的思考与调研

    平时习惯了用js操作dom树来与html页面进行交互,基本都是通过web API接口实现的,最近看闭包和原生js的知识点比较多,昨天无意中看到了onclick中的this指向问题,遂用native j ...

  9. Html 内嵌 选择器属性 Dom操作 JavaScript 事件

    HTML标签: 一.通用标签(一般标签) 1.格式控制标签 <font color="#6699aa" face="楷体" size="24&q ...

随机推荐

  1. android获取https证书

    最近碰到一个问题, 有朋友问android这边能不能拿到服务器下发的证书,意思就是   自签名证书的https接口,在请求的时候,也没有添加自签名证书进信任列表,直接去发https请求,按照正常htt ...

  2. 真正理解 git fetch, git pull 以及 FETCH_HEAD（转）

    转自http://www.cnblogs.com/ToDoToTry/p/4095626.html 真正理解 git fetch, git pull 要讲清楚git fetch,git pull,必须 ...

  3. 怎么旋转PDF文件的方向并保存成功

    http://jingyan.baidu.com/article/59a015e39d7802f79488651e.html PDF格式的文档是非常普遍的一种阅读电子书格式,基本上非常好用了,不过有时 ...

  4. maven+jenkins发布环境

    安装java省略,下面是环境变量 export JAVA_HOME=/usr/java/jdk1.8.0_65/ export PATH=$JAVA_HOME/bin:$PATH export CLA ...

  5. JavaWeb中五种转发方式（转）

    今天本来是想找一下在jsp中实现转发的方式的,无意中看到了一篇文章,然后稍微综合了把服务器端的转发也包括在内.   1. RequestDispatcher.forward() 是在服务器端起作用,当 ...

  6. hihocoder 1093 SPFA算法

    题目链接:http://hihocoder.com/problemset/problem/1093 , 最短路的SPFA算法. 由于点的限制(10w),只能用邻接表.今天也学了一种邻接表的写法,感觉挺 ...

  7. linux 命令——39 grep (转）

    Linux系统中grep命令是一种强大的文本搜索工具,它能使用正则表达式搜索文本,并把匹 配的行打印出来.grep全称是Global Regular Expression Print,表示全局正则表达 ...

  8. Kibana功能一览

    Overview标签 总共32个请求,最大响应时间:4.7秒 Usage标签 可以看到HTTP请求的发起时间分布 Performance and Quality 6个请求里,响应时间在100毫秒以下的 ...

  9. .net reflector 的缺陷

    .net reflector是一个反编译DLL的工具,在安装后如果电脑上有VS也会同时安装到VS里面,但是他是收费的,虽然反编译的效果很好,但是运行VS2013时(或许其他版本也有这样的问题)如果项目 ...

  10. 【POJ2774】Long Long Message（后缀数组求Height数组）

    点此看题面 大致题意: 求两个字符串中最长公共子串的长度. 关于后缀数组 关于\(Height\)数组的概念以及如何用后缀数组求\(Height\)数组详见这篇博客:后缀数组入门(二)--Height ...