Find hash (“#”) in XRegExp with comments

Question

If you use the 'x' flag of XRegExp, it is unclear how to add the literal '#' to the search.

The documentation does not appear to yield any illumination.

For example:

> XRegExp("the # hey",'x').toString()
'/the(?:)/'

This is as expected - everything after '#' is a comment and ignored.

The apparent solution, not ignoring the # and following contents on that line, would usually be (based on my limited experience) leading with an escape modifier, eg \\:

> XRegExp("the \# hey",'x').toString()
'/the(?:)/'

or

> XRegExp("the \\# hey",'x').toString()
'/the(?:)\\#(?:)hey/'

Unfortunately neither works as expected, the prior for obvious reasons, and the latter yields:

> XRegExp("the \\# hey",'x').xtest("the # hey")
false

or even in the more pernicious case that we must modify input data:

> XRegExp("the \\# hey",'x').xtest("the \\# hey")
false

The alternative canonical escaping would be using a double-hash (##), but that does not work either:

> XRegExp("the ## hey",'x').toString()
'/the(?:)/'

So the question becomes, how can one add a # literal to an XRegExp expression that uses the 'x' flag? I'm stumped.

Answer 1

I found the answer and please note that my tests above would not work because the spaces should be replaced by \\s+.

The answer seems to be to use [#] e.g.

> XRegExp("the\\s+[#]\\s+hey",'x').xtest("the # hey")
true

Answer 2

The documentation for flag x is at http://xregexp.com/flags/#extended.

One of the effects of x is that whitespace in your regex pattern is ignored. I see you've discovered that the literal spaces in your regex can be replaced with \s (\\s when embedded in a string literal due to string escaping rules). But note that that's changing your pattern from matching just a space char to matching any whitespace char. Alternatively you could just escape the spaces: XRegExp('the\\ \\# \\ hey', 'x'). Or you could use [ ] in the same way you used [#]. Or you could do something like XRegExp('the' + XRegExp.escape(' # ') + 'hey', 'x'). Or just not use the x flag if you have literal whitespace and # chars in your pattern.