[翻译]High Performance JavaScript(019)
第六章 Responsive Interfaces 响应接口
There's nothing more frustrating than clicking something on a web page and having nothing happen. This problem goes back to the origin of transactional web applications and resulted in the now-ubiquitous "please click only once" message that accompanies most form submissions. A user's natural inclination is to repeat any action that doesn't result in an obvious change, and so ensuring responsiveness in web applications is an important performance concern.
没有什么比点击页面上的东西却什么也没发生更令人感到挫折了。这个问题又回到了原始网页交互程序和现在已无处不在的提交表单时弹出的“请勿重复提交”消息上面。用户自然倾向于重复尝试这些不发生明显变化的动作，所以确保网页应用程序的响应速度也是一个重要的性能关注点。
Chapter 1 introduced the browser UI thread concept. As a recap, most browsers have a single process that is shared between JavaScript execution and user interface updates. Only one of these operations can be performed at a time, meaning that the user interface cannot respond to input while JavaScript code is executed and vice versa. The user interface effectively becomes "locked" when JavaScript is executing; managing how long your JavaScript takes to execute is important to the perceived performance of a web application.
第一节介绍了浏览器UI线程概念。总的来说，大多数浏览器有一个单独的处理进程，它由两个任务所共享：JavaScript任务和用户界面更新任务。每个时刻只有其中的一个操作得以执行，也就是说当JavaScript代码运行时用户界面不能对输入产生反应，反之亦然。或者说，当JavaScript运行时，用户界面就被“锁定”了。管理好JavaScript运行时间对网页应用的性能很重要。
The Browser UI Thread 浏览器UI线程
The process shared by JavaScript and user interface updates is frequently referred to as the browser UI thread (though the term "thread" is not necessarily accurate for all browsers). The UI thread works on a sim
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本文主要是出于有朋友使用我原来写的autocomplete的JS控件。当数据量大的时候，会出现效率极其慢的情况，我在这段时间做出的一些测试也及一些经验，与大家分享，如果有错的地方，还请指出。
经过测试，我们会发现如下的情况或者说的结论，如果您的测试结果与我的不符，请说明原因，以便相互学习。
1）当一个较大的HTML字� ......
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 ......
function total(){
var i=0;
for(j=1;j<=20;j++)
{
var step="step"+j;
if(document.getElementById(step)){
if(document.getElementById(step).checked==true)
{
i=i+parseInt(document.getElementById(step).value);
}
}
}
document.getElementById("total").innerHTML = i;
}
function Resetvalue(){
......
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，JavaScri ......
String Trimming 字符串修剪
Removing leading and trailing whitespace from a string is a simple but common task. Although ECMAScript 5 adds a native string trim method (and you should therefore start to see this method in upcoming browsers), JavaScript has not historically in ......
