SuperHero.prototype = Object.create( Person.prototype );

var Person =  function( firstName , lastName ){
  this.firstName = firstName;
  this.lastName =  lastName;
  this.gender = "male";
};

// a new instance of Person can then easily be created as follows:
var clark = new Person( "Clark" , "Kent" );

// Define a subclass constructor for for "Superhero":
var Superhero = function( firstName, lastName , powers ){

    // Invoke the superclass constructor on the new object
    // then use .call() to invoke the constructor as a method of
    // the object to be initialized.

    Person.call( this, firstName, lastName );

    // Finally, store their powers, a new array of traits not found in a normal "Person"
    this.powers = powers;
};

SuperHero.prototype = Object.create( Person.prototype );
var superman = new Superhero( "Clark" ,"Kent" , ["flight","heat-vision"] );
console.log( superman );

// Outputs Person attributes as well as powers

SuperHero.prototype = new Person();

SuperHero.prototype = Object.create( Person.prototype );

SuperHero.prototype = new Person();

var person = new Person();
SuperHero.prototype = person; // inheritance here
// the Object.create way is ECMAScript 5 (which not all browsers support yet sadly)

var superman = new SuperHero( "Clark" ,"Kent" , ["flight","heat-vision"] );
console.log( person );
console.log( superman ); ​