HTML forms.
Second, the requests themselves are asynchronous,meaning that the
contextual links, zoom control , and the other page features remain
accessible while the map is gathering new data.
The four main components of Ajax:Javascript defines business rules and
program flow. The Document Object Model and Cascading Style Sheets allow
the application to reorgnize its appearance in response to data feteched in
the background from the server by the XMLHttpRequest object or its close
cousins.
We've hightlighted a few more here , to demonstrate the breadth of concerns
to which CSS can be applied:
(1)on-screen placement
(2)texturing elements
(3)assisting in layout of elements
(4)placing text relative to accompanying graphics
The DOM presents an HTML document as a tree structure , with each element
representing a tag in the HTML markup.
Working with the DOM using Javascript
An Example:
window.onload=function(){
var hello=document.getElementById('hello');
hello.className='declared';
var empty = document.getElementById('empty');
addNode(empty,"reader of");
addNode(empty,"Ajax in action");
var children = empty.childNodes;
for (var i=0;i<children.length;i++){
children[i].className='programmed';
}
empty.style.border='solid green 2px';
empty.style.width='200px';
}
function addNode(el,text){
var childEl = document.createElement('div'); --create new element
el.appendChild(childEl);
var txtNode=document.createTextNode(txt); --create text element
childEl.appendChild(txtNode);
}
A third method worth mentioning allows us to make a shortcut through
documets that we haven't tagged with unique IDs. DOM nodes can also be
searched for based on their HTML tag type,usinf getElementByTagName(). For
example , document.getElementByTagName('UL') will return an array of all
<UL> tags in the document.
FINDING A DOM NODE
CREATING A DOM NODE
Adding styles to your document:
hello.className='declared';
empty.style.border="solid green 2px";
innerHTML
refactoring 重构
Working with DOM elements
A web page is exposed to Javascript through the Document Object Model
(DOM),a tree-like structure whose elements correspond to the tags of an
HTML document. When manipulating a DOM tree progarmmatically ,it is quite
common to want to find out an element's position on the page.
Unfortunately,browser vendors have provided various nonstandard methods for
doing so over the years,making it diffcult to write fail-safe cross-browser
code to accommplish the task.
window.onloadListeners = new Array();
window.addOnLoadListener(listener){
window.onloadListener[window.onloadListeners.length]=listener;
}
window.onload=function(){
for(var i=0;i<window.onloadListeners.length;i++){
var func = window.onloadListeners[i];
}
}
//------------------------------------------
Reusing user action handlers:命o模式
function buttonOnClickHandler(event){
var data = new Array();
data[0]=6;
data[1]=data[0]/3;
data[2]=data[0]*data[1]+7;
var newRow = createTableRow(dataTable);
for (var i=0;i<data.length;i++){
createTableCell(newRow,data[i]);
}
}
buttonDiv.onclick=buttonOnClickHandler;
//------------------------------------
Keeping only one reference to a resource:Singleton pattern
function TradingMode(){
this.mode=MODE_RED;
}
TradingMode.prototype.setMode=function(){
}
TradingMode.instance = new TradingMode();
var TradingMode={
mode:MODE_RED,
setMode:function(){
...
}
};
Z模板的系l：
Prototype:
Prototype是一个ؓJavascript~程提供多用途的助手cdQ用一个导向扩?/P>
Javascript语言自己支持一个OO~程方式。Prototype有一个有特色的Javascript~码
样式Q基于这些已l增加的语言Ҏ。虽然Prototype~码自n很难阅读Q从Java/C#/
样式中被U除存在很久了，使用PrototypeQ和内徏在它上的Q是直接的。Prototype
可以考虑为类开发者提供类。AJax应用E序作者更多希望用类建立c而不是?/P>
Prototype自n。我们将查询q些cd下面的部分中。在期间Q一个主要的关于
Prototype核心的特性讨论将帮助介绍它自w的~码的样式和在我们讨论
Scriptaculous、Rico和Rubt on Rail.
Prototype允许一个对象扩展通过复制所有的父对象的属性和Ҏl子其他。这?/P>
Ҏ是最好的举个例子,让我们看一下定义的Vehicle父类
function Vehicle(numWheels,maxSpeed){
this.numWheels = numWheels;
this.maxSpeed = maxSpeed;
}
Ҏ我们惌定义一个精的实例来表C个乘客列车。在我们的子cM我们也想?/P>
现客车的数量q支持增加或减少的机制。在常用的Javascript中，我们可能q样写：
var passTrain = new Vehicle(24,100);
passTrain.carriageCount = 12;
passTrain.addCarriage = function(){
this.carriageCount++;
}
passTrain.removeCarriage=function(){
this.carriageCount--;
}
qؓ我们的PassTrain对象提供需要的功能性。从设计的视囄查看q些代码Q虽然它
有点掩饰了扩展扩展性功能性到一个连贯的单元。Prototyp可以在这里帮助我们，?/P>
q允许我们定义扩展行ZZ个对象ƈ且接着使用它扩展基对象。首先，我们?/P>
Z个对象定义扩展的功能性：
function CarriagePuller(carriageCount){
this.carriageCount = carriageCount;
this.addCarriage=function(){
this.carriageCount++;
}
this.removeCarriage=function(){
this.carriageCount--;
}
}
接着我们合ƈq两个来支持一个对象包含所有的需要的行ؓQ?BR>var parent = new Vehicle(24,100);
var extension = new CarriagePuller(12);
var passTrain = Object.extend(parent,extension);
注意我们分别在开始后来定义父和扩展对象，接着他们进行合。这父子关系存在
q些例中Q不在Vehicle和CarriagePullercM。当它不是正的l典的面向对象，?/P>
允许我们保持我们代码与系l功能进行关联，在这个拉车按例中Q在一个地方，通过
在我们更Ҏq行复用。我们做q个例子看v来似乎没有什么用处，在大的项目中Q?/P>
用这U方法封装功能性是非常有用的?/P>
Prototype也以AJax对象的方式提供对Ajax支持Q这可以解决^台XMLHttpRequest?/P>
象。Ajax是被Ajax.Requestcd扩展Q它可以使用XMLHttpRequest向服务器发送请?/P>
Q例如： var req = new Ajax.Request('myData.xml');
q个构造子使用一个我们也要看到的在很多Prototype-basedcd中的样式。它使用
l合的数l来作ؓ一个可选的参数Q允怸个宽范围的按照需要进行配|?/P>
Ajax.Updater
The View in an Ajax application
Keepling the logic out of the View View分离出logic
间接使用CSS增加事g
l定事g控制代码
The Rico framework has a concept of Behavior objects that target specific
sections of a DOM tree and add interactivity to them.
Keeping the view out of logic
]]>