Question

现在，此部分代码未定义传递到if(customerWaiting >0)。我似乎无法弄清楚这是异步的问题。

基于我看过的其他线程，这是一个非常基本的问题，也是一个新手问题，我无法使其正常工作。

我在看你是否能找到我

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，则表明没有客户在等待

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

这是代码

 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");
  }
});

Answer 1

如果我对您的理解正确，那么您想这样做：

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");
    }
  });
});

如果您想使用await / async，那么ref.child("customerWaiting").on("value", resolve)必须支持Promises，或者您需要将其转换为一个：

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");
  }
});

javascript If / Else循环；异步问题

1 个答案: