了解命名访问器属性属性

Question

At 8.6.1 sec. the attributes of named accessor property are given. Let we are creating named accessor property such as

var o=Object.create({},{bar:{get: function(){ return 10;}, 
                             set: function(value){ console.log("o.bar is", value)}}})
o.bar=550;

It's ok. In console we have o.bar is 550 . But i have a some doubts. Named accessor property doesn't have value attribute. So which attribute is assigned to 550?

How we can return this assigned value? I'm trying to rewrite get function such the following:

get: function(){ return value;}

But I have error:

[15:59:41.418] ReferenceError: value is not defined @ http://fiddle.jshell.net/_display/:26

Please explain me how named accessor property works?

Answer 1

Named accesor property doesn't have value attribute. So which attribute is assigned to 550?

None, you have to do that in your setter. It's not done automatically.

How we can return this assigned value?

From wherever you saved it. For instance, it's fairly common to use a closure for this (I've put it on multiple lines for clarity) :

var o=Object.create({},(function() {
    var _bar = 10;

    return {
      bar:{
        get: function(){
          return _bar;
        },
        set: function(value){
          _bar = value;
          console.log("bar set to " + _bar);
        }
      }
    };
})());
o.bar=550;
console.log("o.bar = " + o.bar);

Live Example | Source

Condensed version if you're into that sort of thing: :-)

var o=Object.create({},(function() {
    var _bar = 10;

    return {bar:{get: function(){ return _bar; },
                 set: function(value){ _bar = value; console.log("bar set to " + _bar); }}};
})());
o.bar=550;
console.log("o.bar = " + o.bar);