Simplify the wrapRegExp helper for named groups

[nicolo-ribaudo]

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

• The possibleConstructorReturn helper dependency was unused.
• We don't need wrapNativeSuper, since we can use new RegExp and then manually set the result prototype.

When compiling this code:

export let re = /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/;

This was the old output (4.3kB, 2.3kB minified)

function _wrapRegExp(re, groups) { _wrapRegExp = function (re, groups) { return new BabelRegExp(re, undefined, groups); }; var _RegExp = _wrapNativeSuper(RegExp); var _super = RegExp.prototype; var _groups = new WeakMap(); function BabelRegExp(re, flags, groups) { var _this = _RegExp.call(this, re, flags); _groups.set(_this, groups || _groups.get(re)); return _this; } _inherits(BabelRegExp, _RegExp); BabelRegExp.prototype.exec = function (str) { var result = _super.exec.call(this, str); if (result) result.groups = buildGroups(result, this); return result; }; BabelRegExp.prototype[Symbol.replace] = function (str, substitution) { if (typeof substitution === "string") { var groups = _groups.get(this); return _super[Symbol.replace].call(this, str, substitution.replace(/\$<([^>]+)>/g, function (_, name) { return "$" + groups[name]; })); } else if (typeof substitution === "function") { var _this = this; return _super[Symbol.replace].call(this, str, function () { var args = []; args.push.apply(args, arguments); if (typeof args[args.length - 1] !== "object") { args.push(buildGroups(args, _this)); } return substitution.apply(this, args); }); } else { return _super[Symbol.replace].call(this, str, substitution); } }; function buildGroups(result, re) { var g = _groups.get(re); return Object.keys(g).reduce(function (groups, name) { groups[name] = result[g[name]]; return groups; }, Object.create(null)); } return _wrapRegExp.apply(this, arguments); }

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function"); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, writable: true, configurable: true } }); if (superClass) _setPrototypeOf(subClass, superClass); }

function _possibleConstructorReturn(self, call) { if (call && (typeof call === "object" || typeof call === "function")) { return call; } return _assertThisInitialized(self); }

function _assertThisInitialized(self) { if (self === void 0) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return self; }

function _wrapNativeSuper(Class) { var _cache = typeof Map === "function" ? new Map() : undefined; _wrapNativeSuper = function _wrapNativeSuper(Class) { if (Class === null || !_isNativeFunction(Class)) return Class; if (typeof Class !== "function") { throw new TypeError("Super expression must either be null or a function"); } if (typeof _cache !== "undefined") { if (_cache.has(Class)) return _cache.get(Class); _cache.set(Class, Wrapper); } function Wrapper() { return _construct(Class, arguments, _getPrototypeOf(this).constructor); } Wrapper.prototype = Object.create(Class.prototype, { constructor: { value: Wrapper, enumerable: false, writable: true, configurable: true } }); return _setPrototypeOf(Wrapper, Class); }; return _wrapNativeSuper(Class); }

function _construct(Parent, args, Class) { if (_isNativeReflectConstruct()) { _construct = Reflect.construct; } else { _construct = function _construct(Parent, args, Class) { var a = [null]; a.push.apply(a, args); var Constructor = Function.bind.apply(Parent, a); var instance = new Constructor(); if (Class) _setPrototypeOf(instance, Class.prototype); return instance; }; } return _construct.apply(null, arguments); }

function _isNativeReflectConstruct() { if (typeof Reflect === "undefined" || !Reflect.construct) return false; if (Reflect.construct.sham) return false; if (typeof Proxy === "function") return true; try { Boolean.prototype.valueOf.call(Reflect.construct(Boolean, [], function () {})); return true; } catch (e) { return false; } }

function _isNativeFunction(fn) { return Function.toString.call(fn).indexOf("[native code]") !== -1; }

function _setPrototypeOf(o, p) { _setPrototypeOf = Object.setPrototypeOf || function _setPrototypeOf(o, p) { o.__proto__ = p; return o; }; return _setPrototypeOf(o, p); }

function _getPrototypeOf(o) { _getPrototypeOf = Object.setPrototypeOf ? Object.getPrototypeOf : function _getPrototypeOf(o) { return o.__proto__ || Object.getPrototypeOf(o); }; return _getPrototypeOf(o); }

export let re = /*#__PURE__*/_wrapRegExp(/([0-9]{4})\x2D([0-9]{2})\x2D([0-9]{2})/, {
  year: 1,
  month: 2,
  day: 3
});

This is the new output (2.1kB, 1.2kB minified)

function _wrapRegExp() { _wrapRegExp = function (re, groups) { return new BabelRegExp(re, undefined, groups); }; var _super = RegExp.prototype; var _groups = new WeakMap(); function BabelRegExp(re, flags, groups) { var _this = new RegExp(re, flags); _groups.set(_this, groups || _groups.get(re)); return _setPrototypeOf(_this, BabelRegExp.prototype); } _inherits(BabelRegExp, RegExp); BabelRegExp.prototype.exec = function (str) { var result = _super.exec.call(this, str); if (result) result.groups = buildGroups(result, this); return result; }; BabelRegExp.prototype[Symbol.replace] = function (str, substitution) { if (typeof substitution === "string") { var groups = _groups.get(this); return _super[Symbol.replace].call(this, str, substitution.replace(/\$<([^>]+)>/g, function (_, name) { return "$" + groups[name]; })); } else if (typeof substitution === "function") { var _this = this; return _super[Symbol.replace].call(this, str, function () { var args = []; args.push.apply(args, arguments); if (typeof args[args.length - 1] !== "object") { args.push(buildGroups(args, _this)); } return substitution.apply(this, args); }); } else { return _super[Symbol.replace].call(this, str, substitution); } }; function buildGroups(result, re) { var g = _groups.get(re); return Object.keys(g).reduce(function (groups, name) { groups[name] = result[g[name]]; return groups; }, Object.create(null)); } return _wrapRegExp.apply(this, arguments); }

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function"); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, writable: true, configurable: true } }); if (superClass) _setPrototypeOf(subClass, superClass); }

function _setPrototypeOf(o, p) { _setPrototypeOf = Object.setPrototypeOf || function _setPrototypeOf(o, p) { o.__proto__ = p; return o; }; return _setPrototypeOf(o, p); }

export let re = /*#__PURE__*/_wrapRegExp(/([0-9]{4})\x2D([0-9]{2})\x2D([0-9]{2})/, {
  year: 1,
  month: 2,
  day: 3
});

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/45619/

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[JLHwung]

nit: We can also hoist _super[Symbol.replace] if we want to golf a bit.

[nicolo-ribaudo]

Not caching it makes it possible to monkey-patch RegExp.protototype[Symbol.replace], similarly to how its possible with native regexps.

[jridgewell]

Nit:

Suggested change

	var args = [];
	args.push.apply(args, arguments);
	var args = [].slice.call(arguments);

[jridgewell]

I think this is incorrect. Because we transform (?<year>\d{4}) to ([0-9]{4}), if there is a object here, it won't include the year group. I think we ned to pop and push if there's an object, and only push if there's not.

[nicolo-ribaudo]

The object here is not the one internally built by the engine, but it's the .groups property returned by our exec() (which defined .groups.year.

[nicolo-ribaudo]

You can verify it with

class MyRegExp extends RegExp {
  exec() {
    return Object.assign(["a", "b"], { groups: { name: "c" } });
  }
  [Symbol.replace](str, subst) {
    super[Symbol.replace](str, (...args) => {
      console.log(args);
      return "_";
    });
  }
}
"abc".replace(new MyRegExp("b"));

[jridgewell]

Crazy, I didn't realize it was accessing the .groups directly from result.

[nicolo-ribaudo]

One more perf reason that makes implementers hate regexp subclasses 😛

[jridgewell]

Crazy, I didn't realize it was accessing the .groups directly from result.