TypeError：promise.then不是函數

Question

使用Rxjs v5，嘗試按順序運行http.get請求但得到錯誤TypeError: promise.then is not a function js代碼：

    var http = require('http');
    Rx.Observable
        .from(data)
        .pairwise()
        .concatMap(a => {
            var url = 'http://to/some/api?origins=' + a[0].lat + ',' + a[0].lng + '&destinations=' + a[1].lat + ',' + a[1].lng;
            return Rx.Observable.fromPromise(http.get(url));        
        })    
        .subscribe(item => {
            console.log(item);
        });

Answer 1

節點http.get方法不返回promise，請參見此處

它實際上使用了一個相當非標准的界面（至少我以前沒有真正看過它），所以要實現這個，你需要一個小的自定義解決方案（ 注意 ：這是一個相對天真的實現）：

var http = require('http');
function observableGet(options) {
  return new Rx.Observable(subscriber => {
    var subscription = new Rx.Subscription();

    //Create the request
    var request = http.get(options, (res) => {
      //Create a stream for the "end" event
      var done = Rx.Observable.fromEvent(res, 'end');

      //Create a stream for data events
      var s1 = Rx.Observable.fromEvent(res, 'data')
        //Take data events until all have been read
        .takeUntil(done)
        //Gather all the data events into a single object
        .reduce((body, delta) => body + delta, '')
        //Optional: Parse the resulting data object
        .map(x => JSON.parse(x))
        //Start the stream
        .subscribe(subscriber);

      //Register this stream for disposal
      subscription.add(s1);
    });

    //Grab errors from the request and forward them to the error handler
    //of subscriber
    var s2 = Rx.Observable.fromEvent(request, 'error', (e) => { throw e; })
      .subscribe(subscriber);

    //Register for disposal
    subscription.add(s2);

    //Return the parent subscription
    return subscription;
  });
}

然后你可以用它代替http.get

    Rx.Observable
    .from(data)
    .pairwise()
    .concatMap(a => {
        var url = //...url;
        return observableGet(url);        
    })    
    .subscribe(item => {
        console.log(item);
    });

或者，您可以使用返回Promises的庫，這可能會讓您的生活更輕松，即請求承諾