Replace all character matches that are not escaped with backslash

Question

I am using regex to replace ( in other regexes (or regexs?) with (?: to turn them into non-matching groups. My expression assumes that no (?X structures are used and looks like this:

(
  [^\\]     - Not backslash character
  |^        - Or string beginning
)
(?:
  [\(]      - a bracket
)

Unfortunatelly this doesn't work in case that there are two matches next to each other, like in this case: how((\s+can|\s+do)(\s+i)?)?

With lookbehinds, the solution is easy:

/(?<=[^\\]|^)[\(]/g

But javascript doesn't support lookbehinds, so what can I do? My searches didn't bring any easy universal lookbehind alternative.

Answer 1

通过逆转使用lookbehind：

function revStr(str) {
    return str.split('').reverse().join('');
}

var rx = /[(](?=[^\\]|$)/g;
var subst = ":?(";

var data = "how((\\s+can|\\s+do)(\\s+i)?)?";
var res = revStr(revStr(data).replace(rx, subst)); 
document.getElementById("res").value = res;

<input id="res" />

请注意，正则表达式模式也是相反的，因此我们可以使用预测而不是后视，并且替换字符串也是相反的。使用更长的正则表达式会变得太棘手，但在这种情况下，它仍然不是那么难以理解。

Answer 2

一种选择是使用令牌进行双程替换（我喜欢unicode，因为它不太可能出现在其他地方）：

＆＃13;

＆＃13;

var s = 'how((\\s+can|\\s+do)(\\s+i)?)?';
var token = "\u1234";
// Look for the character preceding the ( you want
// to replace. We'll add the token after it.
var patt1 = /([^\\])(?=\()/g;
// The second pattern looks for the token and the (.
// We'll replace both with the desired string.
var patt2 = new RegExp(token + '\\(', 'g');

s = s.replace(patt1, "$1" + token).replace(patt2, "(?:");

console.log(s);

＆＃13;

＆＃13;

＆＃13;

https://jsfiddle.net/48e75wqz/1/

Answer 3

（修改）

字符串示例：

how((\s+can|\s+do)(\s+i)?)?

一线解决方案：

＆＃13;

＆＃13;

o='how((\\s+can|\\s+do)(\\s+i)?)?';
alert(o.replace(/\\\(/g,9e9).replace(/\(/g,'(?:').replace(/90{9}/g,'\\('))

＆＃13;

＆＃13;

＆＃13;

结果：

how(?:(?:\s+can|\s+do)(?:\s+i)?)?

当然它适用于字符串如何（（\ s + \(can\) | \ s + do）（\ s + i）？）？