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!

Wiktor Stribiżew · Accepted Answer · 2019-05-24 21:41:45Z

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.

edited May 24, 2019 at 21:41

answered May 24, 2019 at 21:35

Wiktor Stribiżew

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4 Comments

Wiktor Stribiżew Over a year ago

FYI, if you need to also match 100000.12, add \d+ alternative, ^(?:[0-9]{1,3}(?:,[0-9]{3})*|\d+)?\.[0-9]{2}$ (demo).

Dumber_Texan2 Over a year ago

Thanks! I went with this one. ^(?:[0-9]{1,3}(?:,[0-9]{3})*)?\.[0-9]{2}$ Any idea how to not allow something like 000,000.12 or 000.12 or 00.12 or 0.12?

Wiktor Stribiżew Over a year ago

@Dumber_Texan2 ^(?:[1-9][0-9]{0,2}(?:,[0-9]{3})*)?\.[0-9]{2}$, see regex101.com/r/aTgmIu/6

Dumber_Texan2 Over a year ago

Thanks for the help! The answer plus your explanations were spot-on.

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