javascript If/Else循环；异步问题

现在，这段代码正在传递给未定义的if（customerWaiting>0）。这是async的一个问题，我似乎无法理解

根据我看到的其他线程，这是一个非常基本的新手问题，我就是不能让它工作

我在看你能不能帮我找到

编辑1：

代码的目标是查看firebase“customerWaiting”数据库中是否有客户，如果有，则显示模式，如果没有，则表示没有客户在等待

structure for database is 
 customerWaiting
    -Automatically generated ID
     -customer information

这是密码

 var customerWaiting;
 var employeeWaiting;


 var ref = firebase.database().ref();

 $("#connectNextUser").click(function() {
  {
    ref.child("customerWaiting").on("value", function(snapshot) {
      var customerWaiting = snapshot.numChildren();
      console.log("There are " + snapshot.numChildren() + " customers waiting");
    });
    ref.child("employeeWaiting").on("value", function(snapshot) {
      var employeeWaiting = snapshot.numChildren();
      console.log("There are " + snapshot.numChildren() + " employees waiting");
    });
  }
  if (customerWaiting > 0) {
    $("#myModal").modal();
    console.log("connect");
  } else {
    console.log("There are " + customerWaiting + " employees waiting");
    console.log("no connect");
  }
});

---

如果我理解正确，您希望这样做：

var ref = firebase.database().ref();

$("#connectNextUser").click(function() {
  // query how many customers are waiting
  ref.child("customerWaiting").on("value", function(snapshot) {
    // as soon as you have the result  then get the numChildren
    var customerWaiting = snapshot.numChildren();
    console.log("There are " + snapshot.numChildren() + " customers waiting");

    if (customerWaiting > 0) {
      // show the modal if customerWaiting > 0
      $("#myModal").modal();
      console.log("connect");
    } else {
      console.log("There are " + customerWaiting + " employees waiting");
      console.log("no connect");
    }
  });
});

如果要使用

wait

/

async

，则

ref.child（“customerWaiting”）。在（“value”，resolve）

上必须支持承诺，或者需要将其转换为承诺：

var ref = firebase.database().ref();

$("#connectNextUser").click(async function() {

  var snapshot = await new Promise((resolve, reject) => {
    ref.child("customerWaiting").on("value", resolve)
    // you should also handle the error/reject case here.
  })

  var customerWaiting = snapshot.numChildren();
  console.log("There are " + snapshot.numChildren() + " customers waiting");

  if (customerWaiting > 0) {
    $("#myModal").modal();
    console.log("connect");
  } else {
    console.log("There are " + customerWaiting + " employees waiting");
    console.log("no connect");
  }
});

---

customerWaiting

在本地声明，但全局使用（在单击回调中）。这是因为

customerWaiting

仅在

value

事件处理程序中定义，而不是外部

单击

handler。很难确切理解您在这里想要实现什么，但我可以告诉您，嵌套事件处理程序几乎总是一个坏主意。你能提供一个更详细的解释你的目标，以及你正在使用的代码。