CheetSheet

// JSON.stringify() JS代码=>string
let jsonText = JSON.stringify(book); 
let jsonText = JSON.stringify(book,["title","edition"])
let jsonText = JSON.stringify(book,(key,value)=>{return value})
let jsonText = JSON.stringify(book,null,4) // 第3个参数控制字符串缩进
let jsonText = JSON.stringify(book,null,'--') 

// JSON.parse() string=>JS代码
let jsonObj = JSON.parse(jsonText)
let jsonObj = JSON.parse(jsonText,(key,value)=>{})  // 复杂用法

// 特殊应用(深拷贝)
let bookCopy = JSON.parse(JSON.stringify(book))

JSON各关系转换

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// 1. JSON对象
let JsonObj = {
  "items": [
    { "id": 1, "name": "Apples",  "price": "$2" },
    { "id": 2, "name": "Peaches", "price": "$5" }
  ] 
}

// 2. JSON字符串
"{"items":[{"id":1,"name":"Apples","price":"$2"},{"id":2,"name":"Peaches","price":"$5"}]}"

// 3. JavaScript对象(将JSON对象的属性值去除双引号)

🚨JSON对象错误转换为字符串：直接在JSON对象外包一个双引

let JsonString = "{
  "items": [
    { "id": 1, "name": "Apples",  "price": "$2" },
    { "id": 2, "name": "Peaches", "price": "$5" }
  ] 
}"

错误点有两个：1.多层嵌套属性时，要使用单引号。2. 若要包含换行字符串，使用反引号。可如下：

let JsonString = `{
  "items": [
    { "id": 1, "name": "Apples",  "price": "$2" },
    { "id": 2, "name": "Peaches", "price": "$5" }
  ] 
}`
let JavaScringObj = JSON.parse(JsonString)

示例说明

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stringify()

// JS 转换为 string
let book = {
    title: '',
    authors: [
        "人名1","人名2"
    ],
    edition: 4
}

// 写法一
let jsonText = JSON.stringify(book); 
// 结果："{"title":"","authors":["人名1","人名2"],"edition":4}"
// 压缩规则：只有符合要求和语法的才能转换，若有值为undefined时该属性会被跳过

// 写法二：简单过滤
let jsonText = JSON.stringify(book,["title","edition"])
// 写法三：复杂过滤
let jsonText = JSON.stringify(book,(key,value)=>{
    switch(key) {
        case "authors":
            return value.join(",") // 返回字符串
        case "year":
            return 5000; // 重新幅值为500
        case "edition":
            return undefined; // 直接忽略
        default:
            return value; // 将值弹出
    }
})

// 写法四：控制缩进
let jsonText = JSON.stringify(book,null,4)
// 写法五：将空白缩进替换为指定字符串
let jsonText = JSON.stringify(book,null,'--')

parse()

// 写法一：简单还原(若是字符串不符合规范会报错)
let jsonObj = JSON.parse(jsonText)
// 写法二：复杂还原
let book = {
    title: "Professional JavaScript", authors: [
        "Nicholas C. Zakas",
        "Matt Frisbie"
    ], edition: 4, 
    year: 2017, 
    releaseDate: new Date(2017,11,1) // stringify会将Date对象转换为日期字符串
}; 
let jsonText = JSON.stringify(book);
let bookCopy = JSON.parse(jsonText, (key, value) => key == "releaseDate" ? new Date(value) : value); // 重新创建Date对象
alert(bookCopy.releaseDate.getFullYear());