JSON serialization and parsing

1、JSON The top level supports three types of values

2、 Basic use

const obj = {
    
  name: "chen",
  age: 23,
  friends: {
    
    name: "feng",
  },
  hobbies: [" football "],
};

//  We need to use JSON.stringify():
const objstring = JSON.stringify(obj);//  It's essentially a json Format 
//  Store object data localStorage
localStorage.setItem("obj", objstring); //  The key requires a string , What we are passing on is the object , Will be converted to a string 
console.log(localStorage.getItem("obj")); //[object Object],  Unable to restore 

3、json serialize

const obj = {
    
  name: "chen",
  age: 23,
  friends: {
    
    name: "feng",
  },
  hobbies: [" football "],
};

//  demand ： Turn the above object into jSON character string 
// 1、 Direct conversion 
const jsonString1 = JSON.stringify(obj);
console.log(jsonString1); //{"name":"chen","age":23,"friends":{"name":"feng"},"hobbies":[" football "]}

// 2、stringify The second parameter replacer
// 2.1、 Pass in array ： Set what needs to be converted . Put that key Will convert 
const jsonString2 = JSON.stringify(obj, ["name", "friends"]);
console.log(jsonString2); //{"name":"chen","friends":{"name":"feng"}}

// 2.2、 Incoming callback function , It can be done to key/value Intercept 
const jsonString3 = JSON.stringify(obj, (key, value) => {
    
  // return value;
  if (key === "age") {
    
    return value + 1;
  }
  return value;
});
console.log(jsonString3); //{"name":"chen","age":24,"friends":{"name":"feng"},"hobbies":[" football "]}

// 3、stringify The third parameter  space
const jsonString4 = JSON.stringify(obj, null, 2);
console.log(jsonString4);

4、json Parse into objects

const JSONString =
  '{"name":"chen","age":24,"friends":{"name":"feng"},"hobbies":[" football "]}';

//  The second parameter can also be intercepted 
const info = JSON.parse(JSONString, (key, value) => {
    
  if (key === "age") {
    
    return value - 1;
  }
  return value;
});
console.log(info);