For example, to match the first slash after the domain name in the URL.
Intent: Only match '/' in '.com/...' but not any '/' in 'https://'.
url = 'https://example.com/...'; [ url.match( /(?<!/)(?<slash>/)(?!k<slash>).../), // [A] url.match(/(?<!k<slash>)(?<slash>/)(?!k<slash>).../) // [B] ]
The above [A] returns the correct match, but [B] is the kind of expression I want (although it did not match any characters), that is, to use the / character only 1 time in the body of regex literals.
Is there a generalized form of expression similar to [B] (using capturing groups or the like) and using only regular expression literals (instead of using the constructor (RegExp))?
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Answer
You can put a positive lookbehind after an optional character inside a negative lookahead. The lookbehind asserts 2 consecutive slashes (using a reference). This way the lookbehind tests the captured slash position and also the position before. Obviously, when it succeeds, the negative lookahead fails.
/(/)(?!.?(?<=1{2}))/
(feel free to use named captures)
or without captures:
//(?!.?(?<=//))/