thisAnonymousSample.js

var person = {
  firstName: 'Hoang',
  lastName: 'Pham',
  friends : ['Minh', 'Sang', 'Khoa', 'Hoang'],
  showFriend: function() {
    for(var i = 0; i < this.friends.length; i++) 
      console.log(this.firstName + ' have a friend named ' + this.friends[i]);
  },
  showFriendThis: function() {
    this.friends.forEach(function(fr){
      console.log(this.firstName + ' have a friend named ' + fr);
    });
  }
};

person.showFriend(); //Hàm chạy đúng

person.showFriendThis(); // Hàm chạy sai