[翻译]High Performance JavaScript(011)
Repaints and Reflows 重绘和重排版
Once the browser has downloaded all the components of a page—HTML markup, JavaScript, CSS, images—it parses through the files and creates two internal data structures:
当浏览器下载完所有页面HTML标记，JavaScript，CSS，图片之后，它解析文件并创建两个内部数据结构：
A DOM tree
A representation of the page structure
一棵DOM树
表示页面结构
A render tree
A representation of how the DOM nodes will be displayed
一棵渲染树
表示DOM节点如何显示
The render tree has at least one node for every node of the DOM tree that needs to be displayed (hidden DOM elements don't have a corresponding node in the render tree). Nodes in the render tree are called frames or boxes in accordance with the CSS model that treats page elements as boxes with padding, margins, borders, and position. Once the DOM and the render trees are constructed, the browser can display ("paint") the elements on the page.
渲染树中为每个需要显示的DOM树节点存放至少一个节点（隐藏DOM元素在渲染树中没有对应节点）。渲染树上的节点称为“框”或者“盒”，符合CSS模型的定义，将页面元素看作一个具有填充、边距、边框和位置的盒。一旦DOM树和渲染树构造完毕，浏览器就可以显示（绘制）页面上的元素了。
When a DOM change affects the geometry of an element (width and height)—such as a change in the thickness of the border or adding more text to a paragraph, resulting in an additional line—the browser needs to recalculate the geometry of the element as well as the geometry and position of other elements that could have been affected by the change. The browser invalidates the part of the render tree that was affected by the change and reconstructs the render tree. This process is known as a reflow. Once the reflow is complete, the browser redraws the affected parts of the screen in a
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<script>
//写cookies函数 作者：翟振凯
function
SetCookie(name,value)//两个参数，一个是cookie的名子，一个是值
{
var Days = 30;
//此 cookie 将被保存 30 天
var exp = new Date(); //new
Date("December 31, 9998");
......
面向对象的语言多数都支持继承，继承最重要的优点就是代码复用，从而构建大型软件系统。如果一个类能够重用另一个类的属性和或方法，就称之为继承。
从这个角度来看看js的继承方式。js中继承方式与写类方式息息相关。不同的写类方式造成不同的继承方式。各种流行js库继承方式也各不相同。从最简单的
复用开始。
1、构造� ......
隐藏成员变量
在函数体内定义的变量为局部变量，离开函数就挂掉了
在函数体内使用this.成员变量名，则为window对象级变量，即全局变量
故需要这样隐藏成员变量，向外只暴露get、set函数
function testClass(name){
var _firstname=name;
return {
getname : function() {
return _fir ......
常规的方法是将年月日取出，然后分别判断范围，然后就判断闰年2月的天数
可以通过new Date(string)的构造，比较年月日字符是否发生变化判断。
function CheckDate(text) {
if (!text) return false;
text = text.replace(/[\/-]0?/g, "/");
if (!text.match(/^\d{4}\/\d{1,2}\/\d{1,2}$/)) return true;
......
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能在多年来一直被网络开发者所忽略,直到最近Gmail, Google suggest和google Maps的横空出世才使人
们开始意识到其重要性.
这两项被忽视的性能是:
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