function Runner(name) {  

  console.log(this instanceof Rabbit); // => true

  this.name = name;  

}

function Rabbit(name, countLegs) {  

  console.log(this instanceof Rabbit); // => true

  // Indirect invocation. Call parent constructor.

  Runner.call(this, name);

  this.countLegs = countLegs;

}

var myRabbit = new Rabbit('White Rabbit', 4);  

console.log(myRabbit); // { name: 'White Rabbit', countLegs: 4 }