Efficient JavaScript coding
1, 尽可能选择高效的method
e.g.
如果没有必要，可以不用regular expression
String.indexOf, String.lastIndexOf > String.match, String.search, String.replace
2, 面对large loop就要斤斤计较
2.1 Create once, use repeatedly
for( var i = 0, oNode; oNode = oElement.childNodes[i]; i++ ) {
if( oNode.nodeValue.match(/^\s*extra.*free/g) ) {
//this creates the expression
//it will be cached and re-used next time through the loop
}
}
for( var i = 0, oNode; oNode = oElement.childNodes[i]; i++ ) {
if( oNode.nodeValue.match(new RegExp(“^\s*extra.*free”,”g”)) ) {
//this will always create a new copy of the expression,
//and is generally much slower than creating static expressions.
}
}
2.2 Referencing element once, use repeatedly
var _table =$("#tableId")
for (var index in json) {
otherFun(_table, json[index]);
};
3 eval is evil
Eval 或者 new Function() 执行时，浏览器先创建整个scripting环境（就像一个新页面），导入scope chain中所有变量，执行script，gc, 最后导出所有变量到当前环境。（in a word, cost much）另外，js engine还不能对它们进行cache优化。
4 less is more
Less code, short naming
Only add event listener what you need
5 do less
Take a short circuit
e.g
var logger=window.console && window.console.dir
var logger=window.console || {}
less XHR calling
e.g. enable cache for the same request
6 Reduce reflow
每当添加element到document里，browser就会reflow整个页面去计算如何重新定位和渲染。
7，cache
Enable cache for duplicated XHR calling
Enable cache for js script file, so move out jscript from jsp to js file.
Reference:
http://slowjavascript.com/JavaScript_Performance_Rocks_Checklist.pdf
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文章来源:
http://sevenduan.javaeye.com/blog/505272