Here is an regular expression from "Javascript:The Good Parts" book
//Make a regular expression object that matches a javascript string.
var my_regexp = new RegExp("\"(?:\\\\.|[^\\\\\\\"])*\"", 'g');
What this [^\\\\\\\"] expression is matching here?
In JavaScript, strings are surrounded by " (or ', which this regex doesn't support) and \ is used to escape characters that would otherwise have a different meaning.
Now, [^\\\\\\\"] is a character class for characters that aren't \ or ". However because we're using a string literal to define the regular expression the " needs escaping, and because \ has a special meaning within both strings and regular expressions we need to escape them too.
\" starting characters
\\" escape `\` for regex
\\\" escape `"` for regex
\\\\\\" escape `\` for string
\\\\\\\" escape `"` for string
It's simpler if you use ' for the string, or a regex literal. The following are all the same.
new RegExp("\"(?:\\.|[^\\\\\\\"])*\"", "g");
new RegExp('"(?:\\.|[^\\\\\\"])*"', 'g');
/"(?:\.|[^\\\"])*"/g
In fact, " doesn't have a special meaning in a regular expression, so escaping it was not necessary.
/"(?:\.|[^\\"])*"/g
Also note that . isn't either \ or ", so the | construct is pointless. I would guess this is an error, and that it's intended to be \\. - i.e. a \ followed by any character. That would require four \ in the original, not two. Without this correction, the expression won't match strings like "ab\\c".
If we want to support ' as well then things are going to get very complicated, and we probably should just use a simple char-by-char parser, rather than a regular expression.
Unwrapping var my_regexp = new RegExp("\"(?:\\.|[^\\\\\\\"])*\"",'g');:
1: new RegExp("\"(?:\\.|[^\\\\\\\"])*\"",'g');
2: /"(?:\.|[^\\\"])*"/g
^--- this backslash is not really needed, but does not hurt
Matches ", followed by any number of . or not \ and not ", followed by ". Also, since the group has (?:...) - it will not actually capture anything, it will just check that such pattern exists.
For example, in a string I "li.ke" donuts. I "h\ate" potatoes. it will match "li.ke", but will not match "h\ate" because of \.
\\\\..
\ or "