javascript - angular2 - http模块作用域问题-PHP中文网问答

最近在学习angular2，写demo时用到其中的http模块，代码如下

app.loginComponent =
    ng.core.Component({
        selector: 'login',
        templateUrl: 'app/login/login.html',
        providers:[lazyResolveService(['app.loginService'])]
    }).Class({
        constructor: [
            ng.http.Http,
            lazyResolveService(['app.loginService']),
            function (http,service) {
                this.result = 'hello world';
                this.httpService = http;
                this.loginService = service;
                // this.loginService = app.loginServiceInjector.get(app.loginService);
            }
        ],

        login: function (username) {
            //this.loginService.printName(username);
            this.httpService.get('http://localhost:8080/xxx/login')
                    .map(function (res) {
                         var str2 = JSON.parse(res._body);
                         return str2.message.securityMessage;
                    })
                    .subscribe(function (res) {
                        console.log(res);
                        return this.result = 'login';
                    });
            console.log(this.result);
        }
    });

在http.get处理到subscribe()这里代码：

                        console.log(res);
                        return this.result = 'login';

时，发现里面的this.result不是构造器里定义的this.result，而是subscribe()里自己重新定义的this.result，导致最后的console.log(this.result)一直输出‘hello world’.
请问怎么在http请求后的处理函数中获取构造器定义的变量？