Regex working in regex tester but not in JS (wrong matches)

Question

this is actually the first time I encounter this problem. I'am trying to parse a string for key value pairs where the seperator can be a different character. It works fine at any regex tester but not in my current JS project. I already found out, that JS regex works different then for example php. But I couldn't find what to change with mine.

My regex is the following:

[(\?|\&|\#|\;)]([^=]+)\=([^\&\#\;]+)

it should match:

#foo=bar#site=test

MATCH 1
1.  [1-4]   `foo`
2.  [5-8]   `bar`
MATCH 2
1.  [9-13]  `site`
2.  [14-18] `test`

and the JS is:

'#foo=bar#site=test'.match(/[(\?|\&|\#|\;)]([^=]+)\=([^\&\#\;]+)/g);

Result:

["#foo=bar", "#site=test"]

For me it looks like the grouping is not working properly. Is there a way around this?

score 3 · Accepted Answer · answered Sep 26 '16 at 08:52

String#match doesn't include capture groups. Instead, you loop through regex.exec:

var match;
while (match = regex.exec(str)) {
    // Use each result
}

If (like me) that assignment in the condition bothers you, you can use a !! to make it clearly a test:

var match;
while (!!(match = regex.exec(str))) {
    // Use each result
}

Example:

var regex = /[(\?|\&|\#|\;)]([^=]+)\=([^\&\#\;]+)/g;
var str = '#foo=bar#site=test';
var match;
while (!!(match = regex.exec(str))) {
  console.log("result", match);
}

score 1 · Answer 2 · answered Sep 26 '16 at 09:03

I wouldn't rely on a complex regex which could fail anytime for strange reasons and is hard to read but use simple functions to split the string:

var str = '#foo=bar#site=test'

// split it by # and do a loop
str.split('#').forEach(function(splitted){
    // split by =
    var splitted2 = splitted.split('=');
    if(splitted2.length === 2) {
        // here you have
        // splitted2[0] = foo
        // splitted2[1] = bar
        // and in the next iteration
        // splitted2[0] = site
        // splitted2[1] = test
    }
}

Regex working in regex tester but not in JS (wrong matches)

2 Answers2