Question

HI，

我正在使用JSON解析的返回对象集。

{
  "word":[
      "offered",
      "postings"
  ],

  "annotation":[
      ["offered highlighted","this is also given as annotation","This annotation has been added here currently","offering new annotation points","\"offered\" is in the sense of languages"],
      ["my postings","this is new annotation for postings.","my postings","this is posting annotation.... Working for the feature of the annotation."]
  ],

  "user":[
  ["","","vinoth","Anonymous","Vinoth"],
  ["Anonymous","vinoth","Anonymous","Arputharaj"]
  ],

  "id":[
  ["58","60","61","63","68"],
  ["32","57","59","62"]
  ],

  "comment":
  {
    "id58":["first comment","This is a old comment for this annotation","Next level of commenting.","Fourth comment to this annotation","testing"],
    "id61":["this is an old annotation.\r\nMy comment is very bad about this.","Second comment to this annotation"],
    "id57":["I want to add one more comment to this"]
    },

    "commentUser":{
      "id58":["vinoth","Anonymous","Vinothkumar","Vinothkumar","vinoth"],
      "id61":["Anonymous","Commentor"],
      "id57":["vinoth"]
      }
  }

我想知道每个对象和数组的长度。

我使用.length来获取annotation[0].length的长度。我得到了预期的结果，即：5。同样是“用户”＆amp; “ID”。

但是我没有得到“字”，“id58”，“id61”等的长度...... 另外，我想知道comment＆amp;的长度。 commentUser。

请帮助我。

Answer 1

要计算对象具有的属性数，您需要遍历属性，但记得使用hasOwnProperty函数：

var count = 0;
for (var p in obj) {
    if (obj.hasOwnProperty(p)) {
        count++;
    }
}

如果您忘记这样做，您将循环继承属性。如果你（或某些库）已经为Object的原型分配了一个函数，那么所有对象似乎都具有该属性，因此看起来一个项目比它们本质上“更长”。

为避免记住这一点，请考虑使用jQuery的each代替：

var count = 0;
$.each(obj, function(k, v) { count++; });

更新使用当前浏览器：

Object.keys(someObj).length

Answer 2

示例中的密钥word的值（我们称之为obj）是一个数组，因此obj.word.length应为2.

comment和commentUser的值是一个对象，它本身没有长度，因此您需要自己计算：

var length=0;
for(var dummy in obj.comment) length++;

JSON - 查找对象的长度

2 个答案: