获取由firebase返回的数组的长度

Question

数组的.length属性对firebase返回的数组不起作用。下面是返回数组的console.log:

0: Object
1: Object
2: Object
3: Object
4: Object
$$added: function () { [native code] }
$$error: function () { [native code] }
$$moved: function () { [native code] }
$$removed: function () { [native code] }
$$updated: function () { [native code] }
$add: function () { [native code] }
$destroy: function () { [native code] }
$getRecord: function () { [native code] }
$indexFor: function () { [native code] }
$inst: function () { [native code] }
$keyAt: function () { [native code] }
$loaded: function () { [native code] }
$remove: function () { [native code] }
$save: function () { [native code] }
$watch: function () { [native code] }
length: 5
__proto__: Array[0]
concat: function concat() { [native code] }
constructor: function Array() { [native code] }
every: function every() { [native code] }
filter: function filter() { [native code] }
findIndex: function (a){if(null==this)throw new TypeError("Array.prototype.find called on null or undefined");if("function"!=typeof a)throw new TypeError("predicate must be a function");for(var b,c=Object(this),d=c.length>>>0,e=arguments[1],f=0;d>f;f++)if(f in c&&(b=c[f],a.call(e,b,f,c)))return f;return-1}
forEach: function forEach() { [native code] }
indexOf: function indexOf() { [native code] }
join: function join() { [native code] }
lastIndexOf: function lastIndexOf() { [native code] }
length: 0
map: function map() { [native code] }
pop: function pop() { [native code] }
push: function push() { [native code] }
reduce: function reduce() { [native code] }
reduceRight: function reduceRight() { [native code] }
reverse: function reverse() { [native code] }
shift: function shift() { [native code] }
slice: function slice() { [native code] }
some: function some() { [native code] }
sort: function sort() { [native code] }
splice: function splice() { [native code] }
toLocaleString: function toLocaleString() { [native code] }
toString: function toString() { [native code] }
unshift: function unshift() { [native code] }

即使console.log长度属性显示5，但由于某种原因调用长度属性返回0。

编辑:

数组的length属性设置为5，但proto的length属性为0。length属性返回proto下的0值。

Answer 1

请记住，调用$asArray是一个异步操作。

$scope.notes = $firebase(ref).$asArray();
console.log($scope.notes.length); // the data has not loaded yet

在控制台中看到长度为零的原因是，在缓冲日志和打印日志之间，值可能会发生变化，这可能非常容易引起误解。尝试使用断点在值执行时查看它们。

由于数据是异步的，您需要使用$loaded承诺。

$scope.notes.$loaded().then(function(notes) {
   console.log(notes.length); // data is loaded here
});