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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!

Dumber_Texan2
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1 Answers1

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[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.
Wiktor Stribiżew
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