String RegExp matches function

gistfile1.js

/***
  The matches function, similar to String.match(),
  returns an array of sub-groups captured by the given RegExp.
***/

function matches(string, regexp, position, result) {
  position = position || 0;
  result = result || [];

  var match = string.slice(position).match(regexp);

  if (match === null) {
    return result;
  }
  else {
    match.index = position + match.index;
    match.input = string;

    result.push(match)

    return matches(string, regexp, match.index + match[0].length, result);
  }
}

/***
  Optionally add the matches function to the String prototype.
***/
/*
String.prototype.matches = function (regexp, position) {
  return matches(this.toString(), regexp, position);
};
*/

var
  log = console.log,
  assert = console.assert;

var
  testString = 'fooABbar fOoC1bar bazEFbar FooGHbar fooIjbar';
  expectedMatches = [
    {'0': 'fooABbar', '1': 'A', '2': 'B', index: 0, input: testString},
    {'0': 'FooGHbar', '1': 'G', '2': 'H', index: 27, input: testString},
    {'0': 'fooIjbar', '1': 'I', '2': 'j', index: 36, input: testString},
  ],
  actualMatches = matches(testString, /foo([a-z])([a-z])bar/i);

for (var ii = 0; ii < expectedMatches.length; ii++) {
  for (var key in expectedMatches[ii]) {
    assert(expectedMatches[ii][key] === actualMatches[ii][key]);
  }
}

log("Test passed");