why I got this.http.get(...).subscribe is not a function in angular2
<p>My code is </p>

<pre>
    import 'rxjs/Rx';
    ...
    let _this = this;
    return new Promise(function(resolve, reject) {
        _this.http[method](url, data, {
            headers: headers
        })
        .toPromise()
        .then(
            (data) => {
                resolve(data);
            },
            error => {
                reject(error);
            }
        );
    });

</pre>

<p>The "subscribe" not come from my code, looks like it's angular original something.</p>

<p>Error message:</p>

<pre>
EXCEPTION: Error: Uncaught (in promise): TypeError: _this.http.get(...).subscribe is not a function
</pre>