4.JSON

4.1 What is JSON?

JavaScript Object Notation (JavaScript Object Notation) referred JSON, a lightweight data-interchange format. Although it is based on the object literal notation of JavaScript, it is language-independent, unrelated said here meant that no dependencies, not to say that can only be used in the js, and then other languages also can be used.

var student = { 
    "name": '张三',  
    "age": 29,   
    "data":[1,2,3] 
};

4.2 JSON syntax

JSON key-value pairs appear in the form of:

var jsonObject = `{"key1":"value1","key2":"value2"}`

Key: Name value with double quotation marks: value of any type may be used between the key and values: spaced.

The type of value:

    数字（整数或浮点数） 
    字符串（在双引号中） 
    逻辑值（true 或 false） 
    数组（在方括号中） 
    对象（在花括号中） 
    null 
    一个具体的函数或者匿名函数

4.3 JSON uses

JSON syntax for storing and exchanging text messages. Similar to XML. For data transfer between systems.

4.4 JSON advantage

JSON is a lightweight data interchange format JSON text is independent of the language. JSON self-descriptive and easier to read. JSON is smaller than XML, faster, and easier to resolve. JSON formatted data is inherently a Javascript object.

4.5 JSON converting between strings and objects js

4.5.1 General JSON

An object used to store information.

//1.定义json对象
var employee = `{ 
    "id":1,    
    "name":"刘备",
    "age":28,   
    "sex":'男'
}`
// 转成js对象才能通过 对象.属性的形式拿到对应的值
employee = JSON.parse(employee);
//2.获取对象中的数据
console.log(employee.id,employee.name,employee.age);

4.5.2 with an array of JSON

[] Indicates an array in json the employee record contains three objects:

//>>3.定义json数组
var employees = `[ 
   {"id":1,"name":'刘备',"age":28,"gender":'男'},
   {"id":2,"name":'关羽',"age":27,"gender":'男'},
   {"id":3,"name":'张飞',"age":26,"gender":'男'}
]`;
employee = JSON.parse(employee);
for(var i=0; i<employee.length;i++){
    console.log(employee.id, employee.age, employee.gender)
}

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ajax front and rear end interactive principle (4)