为什么这种特殊的JavaScript代码以这种方式工作？

Question

var my_obj = Object.create({}, {
    getFoo: {
        value: function() {
            return this.foo;
        }
    }
});
my_obj.foo = 1;

alert(my_obj.getFoo());

Why is getFoo the function instead of value ?

Answer 1

Because Object.create takes property descriptors as input :

propertiesObject

If specified and not undefined , an object whose enumerable own properties (that is, those properties defined upon itself and not enumerable properties along its prototype chain) specify property descriptors to be added to the newly-created object, with the corresponding property names.

and value means:

value
The value associated with the property. (data descriptors only). Defaults to undefined .

But as getFoo implies, it might be better to define it as accessor property :

var my_obj = Object.create({}, {
    foo: {
        get: function(){ 
            return this._foo; },
        set: function(newValue){ 
            this._foo = newValue; 
        }
    }
});

Answer 2

Actually.. its just because you set value to equal a function.

If you were trying to run that function anonymously, you have to include that after the declaration. Observe:

x = { y : function(){return 2;}}

x.y
function (){return 2;}

x = {y : function(){return 2;}()}

x.y
2 

Note the trailing () after the function declaration.

Sorry for the 1 line code, came right from a javascript console.