title: Firebase: Uncaught Error: Query.equalTo: startAt() or equalTo() previously called
body: <p>I found nothing when I tried to search this error on Google:
  "Uncaught Error: Query.equalTo: startAt() or equalTo() previously called!".</p>
  
  <p>(one result that says nothing)</p>
  
  <p>I'm trying to select X children with name of Toni that are found before lastId.</p>
  
  <p>for example:</p>
  
  <pre><code>Ref:
     -236feg262477
          name: "Toni"
     -9759jj900000
          name: "RVR"
     -969999999999
          name: "Toni"
     -777777777777
          name: "TTT"
     -553333333333
          name: "Toni"
  
  Ref.orderByChild("name")
     .equalTo("Toni")
     .startAt(null, "-969999999999")
     .limitToFirst(1)
     .on('child_added', function (snapshot) {
  
          // do something...
  
  });
  </code></pre>
  
  <p>But I get the error in the title of this topic.</p>
  
  <p>Any help appreciated!</p>