/* example 1 */

function Foo(radius) {
    this.radius = radius;
}

Object.defineProperty(Foo.prototype, "radius", {
    get: function() {
        return this._radius;
    },

    set: function(val) {
        if (!Number.isInteger(val)) {
            console.log("radius must be an integer.");
        }
        this._radius = val;
    }
});

Foo.prototype.area = function() {
    return Math.pow(this.radius, 2) * Math.PI;
};

Foo.draw = function() {
    console.log("drawing a circle with radius " + this.radius);
}

var foo = new Foo(10);
console.log(Object.getOwnPropertyNames(foo));

// ["_radius"]

/* example 2 */

function Bar(radius) {
    this.radius = radius;
}

Object.defineProperty(Bar.prototype, "radius", {
    get: function() {
        return this._radius;
    },

    set: function(val) {
        if (!Number.isInteger(val)) {
            console.log("radius must be an integer.");
        }
        this._radius = val;
    }
});

Bar.prototype = {
    area: function() {
        return Math.pow(this.radius, 2) * Math.PI;
    }
};

Bar.draw = function() {
    console.log("drawing a circle with radius " + this.radius);
}
var bar = new Bar(10);
console.log(Object.getOwnPropertyNames(bar));

// ["radius"]

上面2个例子为什么会有不同的输出？