Private Slots

Claus Reinke claus.reinke at talk21.com
Mon Jan 14 10:21:25 PST 2013


> From the teachability perspective, I'm tired of explaining the closure 
> hack to explain "private" properties. Even to some who are experienced 
> webdevs, I have to explain that they can't access the "private" property 
> through "this.".
> The language needs to evolve to the point where people can write 
> "this[something]" to retrieve private state. Symbols work for that.

Below is a slight variation of the closure "hack" that allows using
private properties through this. The idea is to use the public 'this'
as prototype for the private 'this', using 'bind' to give instance
methods access to the private 'this'

Claus


var MyClass = (function () {

    function MyClass(id) {
       this.id = id;

       var private_this = Object.create(this);  // this and more
       private_this.secret = Math.random().toString();

       this.guess = guess.bind(private_this);
    }

    function guess(guess) {
      var check = guess===this.secret
                ? "I'm not telling!"
                : "That guess is wrong!";
      console.log("("+this.id+"'s secret is: "+this.secret+")");
      console.log(this.id+' says: '+check);
    }

    return MyClass;
})();

var myObj1 = new MyClass("instance1");
var myObj2 = new MyClass("instance2");

console.log(myObj1,myObj2);

var guess = Math.random().toString();
console.log("guessing: "+guess);
myObj1.guess(guess);
myObj2.guess(guess);
 


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