在NodeJS中将Firebase数据库放置在何处

Question

我想在我的Web应用程序中调用这段React JS代码。事实是，尽管我尝试在render()方法中调用它，但这导致了无限循环。然后，我尝试在constructor()内调用它，并调用componentWillUpdate()，但未在其中触发函数。

listenForNewPins() {
  console.log("listening for new segnalazioni...");
  var ref = firebase.database().ref("segnalazioni");
  ref.on("child_added", function(snapshot) {
    console.log("new value under segnalazioni:");
    console.log("fetched:", snapshot.val());
    console.log("---------------------------------");
    snapshot.forEach(function(childSnapshot) {
      var childData = childSnapshot.val();

      if (typeof childData.luogo === "undefined") {
        console.log("undefined, ignoring...");
      } else {
        console.log("Using child data:", childData);
        this.setState({ markers: [...this.state.markers, childData] });
      }
    });
  });
}

这是完整的组件：

import React from "react";
import CustomMap from "./components/CustomMap";
import NavBar from "./components/NavBar";
import firebase from "./Firebase";

export default class App extends React.Component {
  state = {
    markers: []
  };

  constructor() {
    super();
    this.listenForNewPins();
  }

  listenForNewPins() {
    console.log("listening for new segnalazioni...");
    var ref = firebase.database().ref("segnalazioni");
    ref.on("child_added", function(snapshot) {
      console.log("new value under segnalazioni:");
      console.log("fetched:", snapshot.val());
      console.log("---------------------------------");
      snapshot.forEach(function(childSnapshot) {
        var childData = childSnapshot.val();

        if (typeof childData.luogo === "undefined") {
          console.log("undefined, ignoring...");
        } else {
          console.log("Using child data:", childData);
          this.setState({ markers: [...this.state.markers, childData] });
        }
      });
    });
  }

  render() {
    const { markers } = this.state;
    return (
      <div>
        <NavBar />
        <CustomMap markers={markers} />
      </div>
    );
  }
}

有任何提示吗？