一篇文章带你了解JavaScript json 对象

前端进阶者

发布于 2021-01-22 10:10:41

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发布于 2021-01-22 10:10:41

文章被收录于专栏：前端进阶交流

一、对象的语法

JSON 对象被大括号环绕 {}，JSON 对象被写成key/value。

{ "name":"John", "age":30, "car":null }

key必须是字符串，并且value必须是一个有效的JSON数据类型（字符串、数字、对象、数组、布尔值或空），Keys 和 values 由冒号分隔，每个key/value对被逗号分隔。

二、访问对象的值

可以使用点（.）访问对象值。

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>项目</title>
</head>
<body style="background-color: aqua;">

<p>Access a JSON object using dot notation:</p>

<p id="demo"></p>

<script>
var myObj, x;
myObj = {
"name": "John",
"age": 30,
"car": null
};
x = myObj.name;
document.getElementById("demo").innerHTML = x;
</script>


</body>
</html>

还可以使用方括号（[]）访问对象值:

<script>
var myObj, x;
myObj = {
"name": "John",
"age": 30,
"car": null
};
x = myObj["name"];
document.getElementById("demo").innerHTML = x;
</script>

三、循环一个对象

可以使用for-in循环，遍历一个对象。

<script>
var myObj = {
"name": "John",
"age": 30,
"car": null
};
for (x in myObj) {
document.getElementById("demo").innerHTML += x + "<br>";
}
</script>

使用括号表示法访问属性值:

<script>
var myObj, x;
myObj = {
"name": "John",
"age": 30,
"car": null
};
x = myObj["name"];
document.getElementById("demo").innerHTML = x;
</script>

四、嵌套的 JSON 对象

JSON的值可以是另外一个JSON对象。

myObj = {
   "name":"John",
   "age":30,
   "cars": {
       "car1":"Ford",
       "car2":"BMW",
       "car3":"Fiat"
  }
}

您可以访问嵌套的JSON对象使用点符号或括号:

x = myObj.cars.car2;
//or:
x = myObj.cars["car2"];

1. 修改值

你可以使用点表示法修改JSON对象的任何值:

myObj.cars.car2 = "Mercedes";

js完整代码：

<script>
    var myObj, i, x = "";
    myObj = {
      "name":"John",
      "age":30,
      "cars": {
        "car1":"Ford",
        "car2":"BMW",
        "car3":"Fiat"
      }
    }
    myObj.cars.car2 = "Mercedes";

    for (i in myObj.cars) {
        x += myObj.cars[i] + "<br>";
    }

    document.getElementById("demo").innerHTML = x;
</script>

你也可以使用方括号来修改一个JSON对象值:

myObj.cars["car2"] = "Mercedes";

js完整代码：

<script>
  var myObj, i, x = "";
  myObj = {
    "name":"John",
    "age":30,
    "cars": {
      "car1":"Ford",
      "car2":"BMW",
      "car3":"Fiat"
    }
  }
  myObj.cars["car2"] = "Mercedes";

  for (i in myObj.cars) {
      x += myObj.cars[i] + "<br>";
  }

  document.getElementById("demo").innerHTML = x;
</script>

2. 删除对象的属性

使用delete关键字从JSON对象删除一个属性:

delete myObj.cars.car2;

完整代码：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>项目</title>
  </head>
  <body style="background-color: aqua;">

    <p>How to delete properties of a JSON object.</p>

    <p id="demo"></p>

    <script>
      var myObj, i, x = "";
      myObj = {
        "name": "John",
        "age": 30,
        "cars": {
          "car1": "Ford",
          "car2": "BMW",
          "car3": "Fiat"
        }
      }
      delete myObj.cars.car2; //通过语句删除内容。

      for (i in myObj.cars) {
        x += myObj.cars[i] + "<br>";
      }

      document.getElementById("demo").innerHTML = x;
</script>

  </body>
</html>