Can't get RegEx pattern to work correctly in MVC 5 View using Javascript

Question

Here is my pattern. I'm trying to allow numbers and a decimal with two places plus an optional comma with three digits.

var pattern = /^[0-9]+(,\d{3})*\.[0-9]{2}$/;

Allow

100,000.12

10,000.12

1,000.12

100.12

10.12

.12 (can't get this to allow... see below)

Don't allow

abcd

1,,000.12

1,00.12

1,000.0

1,000.

1,000

Here is the test. If I add a ? after [0-9] it works here, but it does not work in my MVC 5 View. The modal doesn't open, so MVC doesn't like it.

^[0-9]?+(,\d{3})*\.[0-9]{2}$

https://regex101.com/r/HwLS7q/1

UPDATE 1

Don't allow

000,000.12, 0.12 etc...

Any help is much appreciated! Thanks!

Answer 1

[0-9]?+ is a pattern that matches 1 or 0 digits possessively, not allowing backtracking into the pattern. JS regex does not support possessive quantifiers, hence the issue.

You need to use

^[0-9]*(?:,[0-9]{3})*\.[0-9]{2}$

Or

^(?:[0-9]+(?:,[0-9]{3})*)?\.[0-9]{2}$

Here, the [0-9]* match zero or more digits and (?:[0-9]+(?:,[0-9]{3})*)? matches an optional sequence of 1+ digits followed with 0+ repetitions of , and 3 digit groups.

See this regex demo.

A more precise pattern would be to restrict the first digit chunk to 1, 2 or 3 digits and make the integer part optional:

^(?:[0-9]{1,3}(?:,[0-9]{3})*)?\.[0-9]{2}$

See the regex demo.

Details

• ^ - start of string
• (?:[0-9]{1,3}(?:,[0-9]{3})*)? - an optional sequence of
  • [0-9]{1,3} - one to three digits
  • (?:,[0-9]{3})* - 0 or more repetitions of
    • , - comma
    • [0-9]{3} - three digits
• \. - dot
• [0-9]{2} - two digits
• $ - end of string.