Examples of eliminating `self = this`

self_this.js

/* WRONG */

function Sobachi(){
  this.prefecture = 'Iwate';
  this.characterName = 'Sobatchi';
  this.friends = [];
}

Sobachi.prototype.addFriends = function(friends){
  var self = this;
  friends.forEach(function(friend){
    if(self.characterName != friend.characterName){
      self.friends.push(friend);
    }
  });
};

this.js

/* RIGHT */

function Sobachi(){
  this.prefecture = 'Iwate';
  this.characterName = 'Sobatchi';
  this.friends = [];
}
 
function addFriend(friend){
  (this.characterName != friend.characterName) && (this.friends.push(friend));
};
 
Sobachi.prototype.addFriends = function(friends){
  friends.forEach(addFriend.bind(this));
};