为什么由 /.../ 创建的 javascript RegExp 可以工作，但通过“new RegExp”创建的相同内容却不能？

我很困惑这里有什么区别以及为什么一个有效而另一个无效。有人可以解释一下吗？

//The string to search through
var str = "This is a string /* with some //stuff in here";

//This one will NOT work, it alerts an empty "match"
var regEx = new RegExp( "(\/\*)", "g" );

//This one also will NOT work (tried just in case escaping was the issue)
var regEx2 = new RegExp( "(/*)", "g" );

//This one DOES work
var regEx3 = /(\/\*)/g;

var match = null;

//Trying the first one, it alerts ","
if ( match = regEx.exec( str ) ) alert( match );

//Trying the second one, it alerts ","
if ( match = regEx2.exec( str ) ) alert( match );

//Trying the third one, it alerts "/*,/*" - it works!
if ( match = regEx3.exec( str ) ) alert( match );

我究竟做错了什么？

\是转义字符strings。因此，要创建一个literal反斜杠作为转义字符常用表达，你需要转义它本身：

var regEx = new RegExp("(/\\*)", "g" );

如果您使用 Chrome 或 Safari（也许也在 Firebug 中），您可以通过在控制台中执行代码轻松查看结果表达式：

> new RegExp( "(/\*)", "g" );
/(/*)/g

> new RegExp( "(/\\*)", "g" );
/(/\*)/g

P.S.：不需要转义字符串中的斜杠（尽管它可能在正则表达式中被忽略）。