javascript - 解析复杂的 JSON 文件 "undefined"

Question

我在尝试解析此 JSON 文件时得到“未定义”:

 {
"responses": [
    {
      "labelAnnotations": [
        {
          "mid": "/m/01yrx",
          "description": "cat",
          "score": 0.9926739,
          "topicality": 0.9926739
        },
        {
          "mid": "/m/01l7qd",
          "description": "whiskers",
          "score": 0.9639658,
          "topicality": 0.9639658
        },
        {
          "mid": "/m/083jv",
          "description": "white",
          "score": 0.9582038,
          "topicality": 0.9582038
        },
        {
          "mid": "/m/0k0pj",
          "description": "nose",
          "score": 0.9425352,
          "topicality": 0.9425352
        },
        {
          "mid": "/m/06z04",
          "description": "skin",
          "score": 0.92025506,
          "topicality": 0.92025506
        }
      ]
    }
  ]
}

此文件是来自 google vision API 的 XMLHttpRequest 的结果，这就是我正在做的打印“描述”字段的操作:

e.onload=function(){
  var i= JSON.parse(e.response);
  value = i.responses[0]["description"];
  alert(value);
};

Answer 1

"undefined"来自下面的语句

value = i.responses[0]["description"];

因为 labelAnnotations 是数组中的一个对象，您将使用它来获取描述

value = i.responses[0].labelAnnotations[0]["description"];