defining getters/setters in an object literal with a self-invoking function javascript

Question

When defining an object literal its possible to use a self-invoking function so the function has access to private variables,

obj={
    value:(function(){
        var private;
        return function(){
            return true;
        }
    }())
};

But is it possible to do the same thing with a getter/setter in an object literal?

obj={
    get value(){
        return value;
    },
    set value(v) {
        value=v;
    }
};

Answer 1

[edit 2022] A pretty old answer.

More actual: you can create a factory function. In the snippet the factory creates an object with (get and set) access (through the closure) to a private variable.

const obj1 = objFactory(`Hello`);
const obj2 = objFactory(`World`);
console.log(`${obj1.privateThing} ${obj2.privateThing}`);
obj1.privateThing = `Goodbye`;
console.log(`${obj1.privateThing} ${obj2.privateThing}`);

function objFactory(somethingPrivate) {
  return {
    get privateThing() { return somethingPrivate; },
    set privateThing(value) { somethingPrivate = value; }
  };
}

The old answer:

Not really. You can also create an Immediately Invoked Function Expression (IIFE) for obj though:

obj = function(){
  var privatething = 'hithere';
  
  return {
    get value() {
      return privatething;
    },
    set value(v) {
      privatething = v;
    }
  };
}();
obj.value; //=> 'hithere';
obj.value = 'good morning to you too';
obj.value; //=> 'good morning to you too'

Answer 2

As per ES6 and later style, default values can also be set in the signature.

const _ = function(_x = 'leafy greens', _y = 'chicken', _z = 'noodle soup') {

  // console.log(_x)

  return {
    _x,
    _y,
    _z,
    get x() { return this._x },
    set x(value) { this._x = value }
  }

}()

console.log(_.x)
_.x = 'beef & pork'
console.log(_.x)

Answer 3

This works.

var obj = {a:1};
console.log(obj.a); //1

Object.defineProperty(obj,"a",{
    get: function(){
        return this.b;
    },
    set: function(x){
        this.b = x;
    },
    configurable:true,
});

obj.a = 10;
console.log(obj); //10
for(var key in obj)
{
    console.log(key)
}

If you don't want the property b to be enumerated while using for...in loop or Object.keys(), just add the line

Object.defineProperty(obj,"b",{enumerable:false})

Note : The above code can also be used as a listener, to detect changes in the property's value. (By implementing the needed function in the set method, after setting the value.)

var obj = {a:1};
console.log(obj.a); //1

Object.defineProperty(obj,"a",{
    get: function(){
        return this.b;
    },
    set: function(x){
        this.b = x;
        console.log("obj.a value has been changed to "+x);
    },
    configurable:true,
});

obj.a = 10;
obj.c = 20;
obj.a = 30;