获取 firebase 返回的数组长度 [英] Get length of an array returned by firebase

问题描述

数组的常用 .length 属性不适用于 firebase 返回的数组.这是返回数组的console.log:

The usual .length property of the array doesn't work on the arrays returned by firebase. Here is the console.log of the returned array:

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 的长度属性显示为 5，但由于某种原因调用长度属性返回 0.

even the console.log length property shows 5 but for some reason calling the length property returns 0.

数组的长度属性设置为 5，但 proto 的长度属性为 0..length 属性返回 proto 下的 0 值.

The length property of the array is set to 5 but the length property of the proto is 0. The .length property returns the 0 value under the proto .

推荐答案

请记住，调用 $asArray 是一个异步操作.

Keep in mind that calling $asArray is an asynchronous action.

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

您在控制台中看到零长度的原因是因为值可能会在日志缓冲和打印之间发生变化，这可能会产生误导.尝试使用断点查看执行时的值.

The reason why you're seeing a zero length in the console is because values can change between buffering of the log and printing it, which can be very misleading. Try using a breakpoint to see the values as they execute.

由于数据是异步的，您需要使用 $loaded 承诺.

Since the data is asynchronous you'll need to use the $loaded promise.

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

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