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【02】

JSON 语法是 JavaScript 语法的子集。

JSON 语法规则

JSON 语法是 JavaScript 对象表示法语法的子集。

  • 数据在名称/值对中
  • 数据由逗号分隔
  • 花括号保存对象
  • 方括号保存数组
  • JSON 名称/值对

    JSON 数据的书写格式是:名称/值对。

    名称/值对包括字段名称(在双引号中),后面写一个冒号,然后是值:

    1. "firstName":"John"

     

    这很容易理解,等价于这条 JavaScript 语句:

    1. firstName ="John"

     

    JSON 值

    JSON 值可以是:

  • 数字(整数或浮点数)(不用加引号)
  • 字符串(在双引号中)
  • 逻辑值(true 或 false)(不用加引号)
  • 数组(在方括号中)
  • 对象(在花括号中)
  • null
  • JSON 对象

    JSON 对象在花括号中书写:

    对象可以包含多个名称/值对:

    1. {"firstName":"John","lastName":"Doe"}

     

    这一点也容易理解,与这条 JavaScript 语句等价:

    1. firstName ="John" lastName ="Doe"

     

    JSON 数组

    JSON 数组在方括号中书写:

    数组可包含多个对象:

    1. {
    2. "employees":[
    3. {"firstName":"John","lastName":"Doe"},
    4. {"firstName":"Anna","lastName":"Smith"},
    5. {"firstName":"Peter","lastName":"Jones"}
    6. ]
    7. }

     

    在上面的例子中,对象 "employees" 是包含三个对象的数组。每个对象代表一条关于某人(有姓和名)的记录。

    JSON 使用 JavaScript 语法

    因为 JSON 使用 JavaScript 语法,所以无需额外的软件就能处理 JavaScript 中的 JSON。
    通过 JavaScript,您可以创建一个对象数组,并像这样进行赋值:

    例子

    1. var employees =[
    2. {"firstName":"Bill","lastName":"Gates"},
    3. {"firstName":"George","lastName":"Bush"},
    4. {"firstName":"Thomas","lastName":"Carter"}
    5. ];

     

    可以像这样访问 JavaScript 对象数组中的第一项:

    1. employees[0].lastName;

     

    返回的内容是:

    1. Gates

     

    可以像这样修改数据:

    1. employees[0].lastName ="Jobs";

     

     

    JSON 文件

  • JSON 文件的文件类型是 ".json"
  • JSON 文本的 MIME 类型是 "application/json"


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