Regex that can match empty string is breaking the javascript regex engine

Question

I wrote the following regex: /\\D(?!.*\\D)|^-?|\\d+/g

I think it should work this way:

\\D(?!.*\\D)    # match the last non-digit
|              


        

Answer 1

You can reorder your alternation patterns and use this in JS to make it work:

var arrTest = '12,345,678.90'.match(/\D(?!.*\D)|\d+|^-?/g);
console.log(arrTest);

var test = arrTest.join('').replace(/\D/, '.');

console.log(test);

//=> 12345678.90

RegEx Demo

This is the difference between Javascript and PHP(PCRE) regex behavior.

In Javascript:

'12345'.match(/^|.+/gm)
//=> ["", "2345"]

In PHP:

preg_match_all('/^|.+/m', '12345', $m);
print_r($m);
Array
(
    [0] => Array
        (
            [0] =>
            [1] => 12345
        )
    )

So when you match ^ in Javascript, regex engine moves one position ahead and anything after alternation | matches from 2nd position omwards in input.