Javascript Regex to match feet inches measurement issue

Question

I am new to regex, and I am trying to create a regular expression to match a string that holds a measurement expressed in feet and inches with the possibility of fractional values in the inches. So far, I have the following expression:

var rex =/\s*(\d+)?\s*(?:'|ft|ft.|feet)?\s*-?\s*(\d+)?\s*(\d+)?\/?(\d+)?\s*(?:''|"|in|in.|inches)?/

To be as flexible as possible I made all the captures optional to set measurements like 1ft or 5'' as valid input data.

var mstring = '5in';
var match = rex.exec(mstring);

The problem is that when the regex is applied, for example to 5in the capture that I get is match[1]='5' while the other three values (match[2], match[3] and match[4]) remain undefined.

Is there a way that the captured values appear in the order they are defined? In the above mentioned case, it will be that match[2]="5in" while match[1], match[3] and match[4] remain undefined.

Answer 1

The trick is in using non-capturing groups around the optional parts and using obligatory subpatterns inside those groups:

var rex =/(?:\s*(\d+)\s*(?:feet|ft\.|ft|'))?(?:\s*-\s*(\d+))?(?:\s*(\d+)\/)?(?:(\d+)\s*(?:inches|in\.|in|''|"))?/

In Group 1, I made (?:feet|ft\.|ft|') obligatory, in Group 2, it is the hyphen -, in Group 3, the slash /, and in Group 4, it is the (?:inches|in\.|in|''|") alternation.

See demo

EDIT:

I do not understand the logic now, but if you want 5 in 5in to appear in the 2nd group, use

(?:\s*(\d+)\s*(?:feet|ft\.|ft|'))?(?:\s*-?\s*(\d+))?(?:\s*(\d+)\/)?(?:(\d+)\s*(?:inches|in\.|in|''|"))?
                                         ^

See Demo 2