Question

Why this regex '^[0-9]+\.?[0-9]*$' match for 12.2 and 12,2 ?

jsFiddle

var dot = '12.2',
    comma = '12,2',
    regex = '^[0-9]+\.?[0-9]*$';

alert( dot.match(regex) );
alert( comma.match(regex) );

While it works on regexpal.com

Answer 1

Because the variable regex is a string the escape sequence \. is just ., which matches any character (except newline). If you change the definition of regex to use RegExp literal syntax or escape the escape character (\\.) then it will work as you expect.

var dot = '12.2'
  , comma = '12,2'
  , regex = /^[0-9]+\.?[0-9]*$/;
      // or '^[0-9]+\\.?[0-9]*$'
alert(dot.match(regex));
alert(comma.match(regex));