Simple JavaScript inheritance

inheritance.js

function Animal() { 
  
  /* properties */ 
  this.isWild = true; 
  this.name = ''; 
  this.sound = '';
  this.height = 0; // cm 
  this.weight = 0; // kg 
  this.speed = 0; // km/h 
  this.age = 0; // years old
  
  /* methods */
  this.cry = function() { 
    console.log(this.name + ' says: ' + this.sound + '!'); 
  }
  this.run = function() { 
    console.log(this.name + ' is running at ' + this.speed + 'km/h!');
  }
  this.eat = function() { 
    console.log(this.name + ' is eating!'); 
  }
  
}

function Cat(){ 
  this.inheritFrom = Animal;
  this.inheritFrom();
}
Cat.prototype = new Animal;

function Dog(){ 
  this.inheritFrom = Animal;
  this.inheritFrom(); 
}
Dog.prototype = new Animal;

//testing...
var kitteh = new Cat();
kitteh.name = "Kitty";
console.log(kitteh instanceof Cat); // should be true
console.log(kitteh instanceof Animal); // should be true