通过使用现有元素创建新字段来修改 JSON 对象答案

【问题标题】：Modifying a JSON object by creating a New Field using existing Elements通过使用现有元素创建新字段来修改 JSON 对象
【发布时间】：2011-09-24 15:53:11
【问题描述】：

我有一个像这样的 javascript 对象：

var obj = {"data":
 [
  {"name":"Alan","height":1.71,"weight":66},
  {"name":"Ben","height":1.82,"weight":90},
  {"name":"Chris","height":1.63,"weight":71}
 ]
 ,"school":"Dover Secondary"
}

如何使用 weight/(height)^2 创建一个名为 BMI 的新字段，以便新对象变为：

var new_obj = {"data":
 [
  {"name":"Alan","height":1.71,"weight":66,"BMI":22.6},
  {"name":"Ben","height":1.82,"weight":90,"BMI":27.2},
  {"name":"Chris","height":1.63,"weight":71,"BMI":26.7}
 ]
 ,"school":"Dover Secondary"
}

【问题讨论】：

标签： javascript

【解决方案1】：

var persons = obj.data;
var new_obj = {data: [], school: obj.school};
for(var i=0; i<persons.length; i++){
    var person = persons[i];
    new_obj.data.push({
        name: person.name,
        height: person.height,
        weight: person.weight,
        BMI: Math.round(person.weight / Math.pow(person.height, 2)*10)/10;
    });
    /* Use the next line if you don't want to create a new object,
       but extend the current object:*/
    //persons.BMI = Math.round(person.weight / Math.pow(person.height, 2)*10)/10;
}

new_obj 初始化后，循环遍历数组obj.data。计算 BMI 并将其与所有属性的副本一起添加到 new_obj。如果您不必复制对象，请查看代码的注释部分。

【讨论】：

重要的是要注意，这不会创建新对象，它会就地修改原始对象。
我明白了.. 感谢您提供这个不错的解决方案 :)
别忘了将BMI四舍五入到小数点后两位：-P

【解决方案2】：

尝试使用此代码，在下面的代码中，我使用相同的对象添加了一个字段。我们还可以通过将现有对象复制到临时变量来获得原始对象的副本

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>Modifying a JSON object by creating a New Field using existing Elements</title>
</head>
<body>
<h2>Modifying a JSON object by creating a New Field using existing Elements</h2>
<script type="text/javascript">
    var obj = { "data":
 [
  { "name": "Alan", "height": 1.71, "weight": 66 },
  { "name": "Ben", "height": 1.82, "weight": 90 },
  { "name": "Chris", "height": 1.63, "weight": 71 }
 ]
 , "school": "Dover Secondary"
    }
    alert(obj.data[0].weight);

    var temp=obj["data"];
    for (var x in temp) {
        var w=temp[x]["weight"];
        var h=temp[x]["height"];
        temp[x]["BMI"] = (w / (h) ^ 2) ;

    }

    alert(obj.data[1].BMI);
</script>
</body>
</html>

【讨论】：

【解决方案3】：

var data = obj['data'];
for( var i in data ) 
{
   var person = data[i]; 
   person.BMI = (person.weight/ Math.pow(person.height, 2)).toFixed(2) ;
}

【讨论】：