Question

My understanding was that the regexp form a{m,n} would match a at most n times. However, the following snippet does not work as I would expect (this is javascript):

/\{{2,2}/.exec ('df{{{df')
// [ '{{', index: 2, input: 'df{{{df' ]

Shouldn’t it return null?

Answer 1

It is matching the text because there are two. That satisfies the requirements your regex specifies. If you want to prevent extras from matching use a negative lookahead: (?!\{).

(?:^|[^{])(\{{2,2}(?!\{))

Then, use the first captured group.

Edit, by the way, the the ,2 in {2,2} is optional in this case, since it’s the same number.

Edit: Added usage example to get rid of first matched character. (Javascript doesn’t support negative lookbehind.

var myRegexp = /(?:^|[^{])(\{{2,2}(?!\{))/g;
var match = myRegexp.exec(myString);
alert(match[1]);