获得列表中的第一个

firebase_first_item.js

function makeList(ref) {
  var fruits = ["banana", "apple", "grape", "orange"];
  for (var i = 0; i < fruits.length; i++) {
    ref.push(fruits[i]);
  }
}
 
function getFirstFromList(ref, cb) {
  ref.startAt().limit(1).once("child_added", function(snapshot) {
    cb(snapshot.val());
  });
}
 
// Running this should popup an alert with "banana".
function go() {
  var testRef = new Firebase("https://example.firebaseIO-demo.com/");
  makeList(testRef);
  getFirstFromList(testRef, function(val) {
    alert(val);
  });
}