javascript - 访问嵌套 json 对象的属性返回未定义

Question

这个问题已经有答案了:

How can I access and process nested objects, arrays, or JSON? (31 个回答)

已关闭 7 年前。

var validCoins = {
      "nickel": {
        "weight": 5.00,
        "diameter": 21.21,
        "thickness": 1.95,
        "value": 0.05
      },
      "dime": {
        "weight": 2.27,
        "diameter": 17.91,
        "thickness": 1.35,
        "value": 0.10
      },
      "quarter": {
        "weight": 5.67,
        "diameter": 24.26,
        "thickness": 1.75,
        "value": 0.25
      }
    };

方法一:

Object.keys(validCoins).forEach(function(coinType) {
      alert(coinType.weight);
}

方法2:

for (var key in validCoins){
//Checking for hasOwnpProperty here doesn't make a difference
        alert(key["weight"]);
    }

这些似乎都不起作用，它返回未定义，我错过了什么？ (我是否必须导入库或其他东西？)我打算使用纯 JavaScript 来做到这一点。

Answer 1

var validCoins = {
      "nickel": {
        "weight": 5.00,
        "diameter": 21.21,
        "thickness": 1.95,
        "value": 0.05
      },
      "dime": {
        "weight": 2.27,
        "diameter": 17.91,
        "thickness": 1.35,
        "value": 0.10
      },
      "quarter": {
        "weight": 5.67,
        "diameter": 24.26,
        "thickness": 1.75,
        "value": 0.25
      }
    };

for (var key in validCoins) {
  if (validCoins.hasOwnProperty(key)) {
    alert(validCoins[key].weight);
  }
}

Fiddle