javascript - 如何在 childsnapshot 完成执行后调用函数

Question

我想在所有子快照执行完毕后调用一个函数，

进一步阐述:

我有一个数据集假设 -kvbd...sd 它有两个子数据集

-kvbd...sd ----------> -fdvdv-...jh ----------> -fgshs..shsh

我想在两个子节点处理完成后调用该函数

----------> -fdvdv-...jh ----------> -fgshs..shsh

我的代码:

dRef
        .once("value")
            .then
              (
                function(snapshot)
                 {

                    snapshot.forEach(                                           
                    function(childsnapshot) 
                        {
                       var data=childsnapshot.val();
                       var Apdate=data.Dateval;                                       


                    for (i = 0; i < sel.options.length; i++)                        
                        {
                            var datein=sel.options[i].value;
                            console.log("check:"+datein);                                                        
                            if(datein==Apdate)                                                                                                                          
                            sel.options[i].disable = true;
                            console.log("Success:!!!!!!");                                                                                                              
                        }                                                       
                             pass();


                         }
                        }
                    }                       
                   );

Answer 1

你可以用Promises尝试这样的事情:

ref.once('value')
  .then(function(snapshot) {
    var myFunctToRunAfter = function () {
      console.info('RUN AFTER THE LOOP')
    }

    return new Promise(function(resolve, reject) {
      snapshot.forEach(function(child) {
        console.log('I am a child ' + child.val())
      })
      /* Call the function after the loop */
      resolve(myFunctToRunAfter())
    })
    .then(function() {
      /* I could do something here */
      console.log(snapshot.val())
      console.info('RUN LAST')
    })
  })

这是一个工作示例:

var config = {
  apiKey: "AIzaSyCDyoPVmi2rLIFtb55eTGYYPMsxFR3uuMs",
  authDomain: "test-514b2.firebaseapp.com",
  databaseURL: "https://test-514b2.firebaseio.com",
  storageBucket: "test-514b2.appspot.com",
  messagingSenderId: "773249287825"
};
firebase.initializeApp(config);

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

ref.once('value')
  .then(function(snapshot) {
    var myFunctToRunAfter = function () {
      console.info('RUN AFTER THE LOOP');
    }
    
    return new Promise(function(resolve, reject) {
      snapshot.forEach(function(child) {
        console.log('I am a child ' + child.val())
      })
      /* Call the function after the loop */
      resolve(myFunctToRunAfter())
    })
    .then(() => {
      /* I could do something here */
      console.log(snapshot.val())
      console.info('RUN LAST')
    })
  })

<script src="https://www.gstatic.com/firebasejs/3.6.9/firebase.js"></script>

Codepen具有相同的工作示例。