MelonJS ES 6 concept

gistfile1.js

class Player extends meEntity {
  constructor(x, y, settings) {
    super(x, y, settings);
  }
  update(dt) {
    super.update(dt);
  }
  onCollision(a, b) {
    return false;
  }
}

// Transpiled to:

"use strict";

var _prototypeProperties = function (child, staticProps, instanceProps) { if (staticProps) Object.defineProperties(child, staticProps); if (instanceProps) Object.defineProperties(child.prototype, instanceProps); };
var _get = function get(object, property, receiver) { var desc = Object.getOwnPropertyDescriptor(object, property); if (desc === undefined) { var parent = Object.getPrototypeOf(object); if (parent === null) { return undefined; } else { return get(parent, property, receiver); } } else if ("value" in desc && desc.writable) { return desc.value; } else { var getter = desc.get; if (getter === undefined) { return undefined; } return getter.call(receiver); } };
var _inherits = function (subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function, not " + typeof superClass); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, enumerable: false, writable: true, configurable: true } }); if (superClass) subClass.__proto__ = superClass; };
var _classCallCheck = function (instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } };

var Player = (function (meEntity) {
  function Player(x, y, settings) {
    _classCallCheck(this, Player);

    _get(Object.getPrototypeOf(Player.prototype), "constructor", this).call(this, x, y, settings);
  }

  _inherits(Player, meEntity);

  _prototypeProperties(Player, null, {
    update: {
      value: function update(dt) {
        _get(Object.getPrototypeOf(Player.prototype), "update", this).call(this, dt);
      },
      writable: true,
      configurable: true
    },
    onCollision: {
      value: function onCollision(a, b) {
        return false;
      },
      writable: true,
      configurable: true
    }
  });

  return Player;
})(meEntity);