Match two quotes not preceded by opening bracket

问题

I need a regex matching all occurrences of two quotes ('') not preceded by opening bracket ((). I did a negative lookahead for the bracket followed by a quote. But why is this not working:

/(?!\()''/g

for example with this string

(''test''test

It should match the second occurrence but not the first one but it matches both.

---

When I use exactly the same solution but with check for new line instead of bracket it works fine:

/(?!^)''/g

With this string:

''test''test

It matches as expected only second occurrence.

Tested here

回答1:

Here is a solution that will work correctly even in case you need to handle consecutive double apostrophes:

var output = "''(''test'''''''test".replace(/(\()?''/g, function($0, $1){
	return $1 ? $0 : 'x';
});
document.body.innerHTML = output;

Here, the /(\()?''/g regex searches for all matches with the ( and without, but inside the replace callback method, we check for the Group 1 match. If Group 1 matched, and is not empty, we use the whole match as the replacement text ($0 stands for the whole match value) and if it is not (there is no ( before '') we just insert the replacement.

回答2:

It's bad that Javascript doesn't support lookback but there is a workaround.

try:

[^\(]('{2,2})

See https://regex101.com/r/gT5jR6/1

来源：https://stackoverflow.com/questions/36838311/match-two-quotes-not-preceded-by-opening-bracket