JSON

JSON对象
JSON对象有两个方法，stringify()和parse()
分别是将js序列化为JSON字符串和将JSON 转化为原生js值

  let book = {
            'name':'names',
            money:12,
            anthors:{
                year:2101,
                age:12,
            },
            edtion:1
        }
        let jsonBook = JSON.stringify(book)
        let parseBook  =JSON.parse(jsonBook)
        console.log(book);
//anthors: {year: 2101, age: 12}
//edtion: 1
//money: 12
//name: "names"
        console.log(jsonBook);
//{"name":"names","money":12,"anthors":{"year":2101,"age":12},"edtion":1}

JSON.stringify()除了实例化对象还可以接收三个参数，第一个参数是过滤器，第二个参数可以是数字或者函数
第二个参数是传的包含字符串的数组的话，JSON字符串返回的是对应的属性

数组

  let book = {
            'name':'names',
            money:12,
            anthors:{
                year:2101,
                age:12,
            },
            edtion:1
        }
       let jsonBook = JSON.stringify(book,['money','edtion'])
        console.log(jsonBook);
        //{"money":12,"edtion":1}

函数

函数接受两个参数key和value,我们可以对应key相应的属性执行操作，
值得注意的是 return undefined 会忽略我的属性，最后在default时候一定要返回我们的value

  let book = {
        name:[
            'name','name1','name2'
        ],
        money: 12,
        anthors: {
          year: 2101,
          age: 12,
        },
        edtion: 1,
      };
      let jsonBook = JSON.stringify(book, (key, value) => {
        switch (key) {
          case "name":
            return value.join(",");
          case "money":
            return 5000;
          case "anthors":
            return undefined
          default: 
          return value
        }
      });
      console.log(jsonBook);
//{"name":"name,name1,name2","money":5000,"edtion":1}

第三个参数 缩进

除了可以传入数字也可以传入字符串
let jsonBook = JSON.stringify(book,null,'--')

 let book = {
        name:[
            'name','name1','name2'
        ],
        money: 12,
        anthors: {
          year: 2101,
          age: 12,
        },
        edtion: 1,
      };
      let jsonBook = JSON.stringify(book,null,4)
      console.log(jsonBook);
  //   {   
    //       "name": [
    //           "name",
    //           "name1",
    //           "name2"
    //       ],
    //       "money": 12,
    //       "anthors": {
    //           "year": 2101,
    //           "age": 12
    //       },
    //       "edtion": 1
    //   }
    {
    //   --"name": [
    //   ----"name",
    //   ----"name1",
    //   ----"name2"
    //   --],
    //   --"money": 12,
    //   --"anthors": {
    //   ----"year": 2101,
    //   ----"age": 12
    //   --},
    //   --"edtion": 1
    //   }