Functional Mixin

fnMix.js

var withWalking = function() {
  this.walk = function() {
    console.log(this.name + ' is walking');
  };
  this.turn = function(direction) { console.log('turning', direction);
  };
  this.stopWalking = function() {
    console.log('stopped walking');
  };
};

function Crocodile(name, gender) {
  this.name = name;
  this.gender = gender;
}

Crocodile.prototype.stalkTourists = function() {
  //..
};

withWalking.call(Crocodile.prototype);

// ---

var croc = new Crocodile('Rifat');
croc.walk();

var withWalkingMehdi = function() {
  this.walk = function() {
    console.log(this.name + ' is running');
  };
};

var croc2 = new Crocodile('Mehdi');
withWalkingMehdi.call(croc2);
croc2.walk();

var croc3 = new Crocodile('Nazmun');
croc3.walk();

nice work done.