RxJS 發出的值沒有通過.pipe(...)

Question

在下面的代碼中，我嘗試構建一個 RxJS pipe 並使用pipe處理主題發出的值。 代碼有效，但結果與我預期的不同。

const rxjs = require("rxjs");
var subject = new rxjs.Subject();

subject
.pipe(rxjs.tap(console.log('tap')))
.subscribe(console.log);

function sendRequest(requestID, cb) {
  var delay = Math.floor(Math.random() * (6 - 3 + 1)) + 5;
  var request = {
    hostname: "httpbin.org",
    headers: { "request-id": requestID },
    path: "/delay/." + delay,
  };
  require("http")
    .get(request, (res) => {
      var body = "";
      res.on("data", function (chunk) { body += chunk; });
      res.on("end", function () { cb(res, body); });
    })
    .end();
}

concurrentRequests(5);
function concurrentRequests(limit) {
  for (var i = 0; i < limit; i++) {
    sendRequest(i, function (res, body) {
      var reqID = JSON.parse(body).headers["Request-Id"];
      subject.next("Concurrent Response #" + reqID + " returned a " + res.statusCode);
    });
  }
}

我的目的是構建一個 pipe 來使用來自 RxJS 庫的Subject處理每個發出的值，當我運行上面的代碼時，我希望得到這個 output：

tap
Concurrent Response #1 returned a 200
tap
Concurrent Response #0 returned a 200
tap
Concurrent Response #2 returned a 200
tap
Concurrent Response #3 returned a 200
tap
Concurrent Response #4 returned a 200

但是 output 是：

tap
Concurrent Response #1 returned a 200
Concurrent Response #0 returned a 200
Concurrent Response #2 returned a 200
Concurrent Response #3 returned a 200
Concurrent Response #4 returned a 200

為什么發出的值沒有通過 pipe？

Answer 1

在

subject.pipe(rxjs.tap(console.log('tap')))

您提供了一個值而不是回調：

subject.pipe(rxjs.tap(() => console.log('tap')))

您執行了console.log('tab')並將undefined的值傳遞給rxjs.tap ，而實際上您想添加一個觀察者。