Transform/runtime: Implement "named capturing groups"

Parser support for named capturing groups has been added in ~issue #28~. It’s an ECMAScript proposal at stage 3.

To be able to use it in older engines, we can translate:

/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/

Into:

new RegExpTree(/(\d{4})-(\d{2})-(\d{2})/, ['year', 'month', 'day']);

The regexpTree creates a lightweight facade wrapper on top of ES6-compatible regexp, and provides the same API (test, exec methods, etc).

class RegExpTree {
  constructor(re, groups) {
    this.re = re;
    this.groups = groups;
  }

  test(string) {
    return this.re.test(string);
  }
 
  exec(string) {
    const result = this.re.exec(string);

    // process `result`, and attach `groups`:
    // result.groups.year -> result[1]
    // result.groups.month -> result[2]
    // etc.
  }
  ...
}

As well as overrides String.prototype.match method to attach group names to the groups property on the match result.

const originalMatch = String.prototype.match;

String.prototype.match = function(regexp) {
  // Simple regexp.
  if (!(regexp instanceof RegExpTree) {
    return originalMatch.call(this, regexp);
  }
  
  // RegExpTree. 
  return regexp.exec(this);
};

[hg42]

yes, named groups count => x=1 y=3.

you can also use [null, 1, "year", 3, "month", "day"], then you simply loop through the array and store names[i]: originalMatch[i] in matches.groups, So, matches.groups["3"] would result in “y”.

[DmitrySoshnikov]

Local runtime support has been added in https://github.com/DmitrySoshnikov/regexp-tree/commit/0e6a9ff70679b15bc475574b2ab361bddadc2d84.