Rxjs 是可观察的。toPromise和Observable.last（）.subscribe是相同的

这两行代码的性能相同吗

Observable.range(1,5).toPromise().then(res => console.log(res))

vs

如果你向上看，你会发现它几乎是一样的

return new Promise((resolve, reject) => {
    let value;
    this.subscribe((x) => value = x, (err) => reject(err), () => resolve(value));
});

return new Promise((resolve, reject) => {
    let value;
    this.subscribe((x) => value = x, (err) => reject(err), () => resolve(value));
});