为什么 JSONObject.length 未定义？
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Why is JSONObject.length undefined?
提问by user2672420
In the code below, JSONObject.lengthis 2:
在下面的代码中，JSONObject.length是 2：
var JSONObject = [{
"name": "John Johnson",
"street": "Oslo West 16",
"age": 33,
"phone": "555 1234567"
}, {
"name": "John Johnson",
"street": "Oslo West 16",
"age": 33,
"phone": "555 1234567"
}];
However, in the code below, JSONObject.lengthis undefined. Why?
但是，在下面的代码中，JSONObject.length是未定义的。为什么？
var JSONObject = {
"name": "John Johnson",
"street": "Oslo West 16",
"age": 33,
"phone": "555 1234567"
};
回答by Doug
JavaScript doesn't have a .length property for objects. If you want to work it out, you have to manually iterate through the object.
JavaScript 没有对象的 .length 属性。如果你想解决这个问题，你必须手动遍历对象。
function objLength(obj){
var i=0;
for (var x in obj){
if(obj.hasOwnProperty(x)){
i++;
}
}
return i;
}
alert(objLength(JSONObject)); //returns 4
Edit:
编辑：
Javascript has moved on since this was originally written, IE8 is irrelevant enough that you should feel safe in using Object.keys(JSONObject).lengthinstead. Much cleaner.
自从最初编写 Javascript 以来，它已经发生了变化，IE8 已经无关紧要，您应该放心使用Object.keys(JSONObject).length。干净多了。
回答by Amol M Kulkarni
The following is actually an array of JSON objects :
以下实际上是一个 JSON 对象数组：
var JSONObject = [{ "name":"John Johnson", "street":"Oslo West 16", "age":33,
"phone":"555 1234567"}, {"name":"John Johnson", "street":"Oslo West 16",
"age":33, "phone":"555 1234567" }];
So, in JavaScript length is a property of an array. And in your second case i.e.
所以，在 JavaScript 中，长度是数组的一个属性。在你的第二种情况下，即
var JSONObject = {"name":"John Johnson", "street":"Oslo West 16", "age":33,
"phone":"555 1234567"};
the JSON object is not an array. So the length property is not available and will be undefined. So you can make it as an array as follows:
JSON 对象不是数组。因此 length 属性不可用且未定义。所以你可以把它做成一个数组，如下所示：
var JSONObject = [{"name":"John Johnson", "street":"Oslo West 16", "age":33,
"phone":"555 1234567"}];
Or if you already have object say JSONObject. You can try following:
或者，如果您已经有对象 say JSONObject。您可以尝试以下操作：
var JSONObject = {"name":"John Johnson", "street":"Oslo West 16", "age":33,
"phone":"555 1234567"};
var jsonObjArray = []; // = new Array();
jsonObjArray.push(JSONObject);
And you do get lengthproperty.
而且你确实得到了length财产。
