一篇文章带你了解JavaScript json 数组

前端进阶者

发布于 2021-01-22 10:34:30

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发布于 2021-01-22 10:34:30

简单说，所谓对象，就是一种无序的数据集合，由若干个“键值对”（key-value）构成。

一、数组作为JSON对象

[ "Ford", "BMW", "Fiat" ]

在JSON中的数组，几乎和在JavaScript中数组相同。

在JSON中，数组的值必须是字符串，数字、对象、数组、布尔值或空.

JavaScript中，数组的值可以是以上所有，再加上其他任何有效的JavaScript表达式，包括函数、日期、和undefined。

二、JSON对象中的数组

数组可以是对象属性的值:

{
"name":"John",
"age":30,
"cars":[ "Ford", "BMW", "Fiat" ]
}

1. 访问数组的值

使用索引号访问数组值:

x = myObj.cars[0];

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 id="demo"></p>

        <script>
            myObj = {
                "name": "John",
                "age": 30,
                "cars": ["Ford", "BMW", "Fiat"]
            }
            x = myObj.cars[0];
            document.getElementById("demo").innerHTML = x;
</script>

    </body>

</html>

2. 遍历数组

你可以使用for-in循环遍历数组:

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

或者可以使用for循环:

for (i = 0; i < myObj.cars.length; i++) {
    x += myObj.cars[i];
}

三、JSON对象中的嵌套数组

数组值也可以是另一个数组，甚至另一个JSON对象:

myObj = {
    "name":"John",
    "age":30,
    "cars": [
        { "name":"Ford", "models":[ "Fiesta", "Focus", "Mustang" ] },
        { "name":"BMW", "models":[ "320", "X3", "X5" ] },
        { "name":"Fiat", "models":[ "500", "Panda" ] }
    ]
 }

访问数组内部的数组, 使用for-in loop循环:

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

  <p>Looping through arrays inside arrays.</p>

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

    var myObj, i, j, x = "";
    myObj = {
        "name":"John",
        "age":30,
        "cars": [
            { "name":"Ford", "models":[ "Fiesta", "Focus", "Mustang" ] },
            { "name":"BMW", "models":[ "320", "X3", "X5" ] },
            { "name":"Fiat", "models":[ "500", "Panda" ] }
        ]
    }
/*访问数组内部的数组, 使用for-in loop循环*/
    for (i in myObj.cars) {
        x += "<h1>" + myObj.cars[i].name + "</h1>";
        for (j in myObj.cars[i].models) {
            x += myObj.cars[i].models[j] + "<br>";
        }
    }

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

1. 修改数组值

使用索引号修改数组:

myObj.cars[1] = "Mercedes";

完整代码：

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>项目</title>
</head>
<body>

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

<script>

    var myObj, i, x = "";
    myObj = {
        "name":"John",
        "age":30,
        "cars":[ "Ford", "BMW", "Fiat" ]
    };
    myObj.cars[1] = "Mercedes";

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

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


</body>
</html>