Character() example in Twine/SugarCube

<<scriptwindow.Character = function(config) {
  this.name = '';
  this.running = 0;
  this.jumping = 0;
  this.climbing_trees = 0;

  this.skill_check = function(attr, dc) {
    if (attr in Object.keys(this) {
      const dieSize = 20; // change this for other kinds of dice
      // Add 1 because otherwise this rolls 0-19
      return (Math.floor(Math.random() * dieSize) + 1 + this[attr]) >= dc;
    } else {
      return this.name + " doesn't have the skill " + attr + '.';
    }
  };

  Object.keys(config).forEach(function(attr) {
    if (attr in Object.keys(this) {
      this[attr] = clone(config[attr]); // you have to do this so changing config[attr] doesn't change Character[attr]
    }
  }, this);
}

Character.prototype.clone = function() {
  return new Character(this);
};

Character.prototype.toJSON = function () {
  let ownData = {};
  Object.keys(this).forEach(function(attr) {
    ownData[attr] = clone(this[attr]);
  }, this);
  return JSON.reviveWrapper('new Character($ReviveData$)', ownData);
};
>>

<<set $You to new Character({
  name: "My Character",
  running: 1,
  jumping: 2,
  climbing_trees: 3
})>>

<<if $You.skill_check("running", 5)>>...