Allow more digit after the first 0 with live input validation regex

Question

I have a regex for some verification on my end. It is

^(?![.,])-?[1-9]*?0?[,.]?([,.]\d+)?$

This regex basically validates a number

• if it starts with 0, a comma or dot must follow
  • Valid => 0.12 or 0,456
  • Invalid => 012.90
• cannot have multiple dot or comma in a row e.g. 12..45
• can only a digit or a comma or a dot e.g. 123, 123.45 or 123,45
• can't start and end with a dot or comma

This regex perfectly works for above points but I got stuck on one case which is I can't type a number like 100 or 101 because it still expects me a dot or comma as regex still treats any zero as the first rule. How do I fix it?

Answer 1

You can use

^(?:0|[1-9]\d*)(?:[.,]\d*)?$

See the regex demo.

Details:

• ^ - start of string
• (?:0|[1-9]\d*) - either
  • 0 - zero
  • | - or
  • [1-9]\d* - one to nine digit and then any zero or more digits
• (?:[.,]\d*)? - an optional sequence of a comma or dot and then zero or more digits.
• $ - end of string.