为什么/.../创建的javascript RegExp工作，但是通过“new RegExp”创建的相同才不是？ [英] Why does a javascript RegExp created by /.../ work but the same created via "new RegExp" does not?

问题描述

我很困惑这里的区别是什么，为什么一个有效，另一个没有。有人可以解释一下吗？

  //搜索
的字符串var str =这是一个字符串/ *有些东西在这里; 
 
 //这个不起作用，它警告一个空的匹配
 var regEx = new RegExp（（（\ / \ *），g）; 
 
 //这个也不起作用（以防万一转移是问题）
 var regEx2 = new RegExp（（/ *），g）; 
 
 //这一个工作
 var regEx3 = /（\ / \ *）/ g; 
 
 var match = null; 
 
 //尝试第一个，它会警告，
 if（match = regEx.exec（str））alert（match）; 
 
 //尝试第二个，它会警告，
 if（match = regEx2.exec（str））alert（match）; 
 
 //尝试第三个，它提醒/ *，/ * - 它有效！ 
 if（match = regEx3.exec（str））alert（match）; 
  

我做错了什么？

解决方案

\ 是字符串中的转义字符。因此，要为正则表达式创建文字反斜杠作为转义字符，您需要将其自身转义：

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

如果您使用Chrome或Safari（也可能在Firebug中），您可以轻松查看结果表达式在控制台中执行代码：

> new RegExp（（/ \ *），g ）;

/（/ *）/ g

< p >> 新的RegExp（（/ \\ *），g）;

/（ / \ *）/ g

PS：无需转义字符串中的斜杠（尽管在正则表达式中可能会被忽略。

I'm confused as to what the difference here is and why one works and the other does not. Can someone explain this?

//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 );

What am I doing wrong?

解决方案

\ is the escape characters in strings. Hence, to create a literal backslash as escape character for the regular expressions, you need to escape it itself:

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

If you use Chrome or Safari (maybe also in Firebug), you can easily see the resulting expression by executing the code in the console:

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

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

P.S.: No need to escape the slash in the string (though it might be ignored in the regex).

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