JavaScript:词法闭包还是别的什么?

考虑一下这个脚本:

function Obj(prop) {
    this.prop = prop;
}

var NS = {
    strings: ['first','second','third'],
    objs: [],
    f1: function() {
        for (s in this.strings) {
            var obj = new Obj(this.strings[s]);
            obj.f2 = function() {
                alert(obj.prop);
            }
            this.objs.push(obj);
        }
    }
}

NS.f1();
NS.objs[0].f2(); // third
NS.objs[1].f2(); // third
NS.objs[2].f2(); // third

不完全是预期的输出,但是当我更新到以下内容时:

function Obj(prop) {
    this.prop = prop;
}

var NS = {
    strings: ['first','second','third'],
    objs: [],
    f1: function() {
        for (s in this.strings) {
            var obj = new Obj(this.strings[s]);
            this.wire(obj); // replaces previous function def
            this.objs.push(obj);
        }
    },
    wire: function(obj) {
        obj.f2 = function() {
            alert(obj.prop);
        } // exact same code and function def as the first example
    }
}

NS.f1();
NS.objs[0].f2(); // first
NS.objs[1].f2(); // second
NS.objs[2].f2(); // third

这似乎管用,我也不知道为什么。有人能启发我吗?谢谢