SOURCE

// JSON.stringfiy模拟
// 考虑类型,boolean,number,string,function 与 array,object 区分
// 忽略类型undefined,null,symbal
// 需要判断前后加", undefined,string,function
function jsonStringfiy (value){
    let val = typeof value
    // console.log(val)
    if(val !== 'object'){
        if(/undefined|string|function/.test(val)){
            value = '"' + value + '"'
        }
        return String(value)
    }else{
        let json = []
        let isA = Array.isArray(value)
        for(let k in value){ 
            let v = value[k]
            if(/undefined|string|function/.test(typeof v)){
                v = '"' + v + '"'
            }else if (typeof v === 'object'){
                v = jsonStringfiy(v)
            }
            // console.log(v)
            json.push((isA ? "" : '"' + k + '":')+ String(v)) 
        }
        return (isA?'[':'{') + String(json) + (isA?']':'}')
    }
}

let a = [1,2,3,4,[5,6,7]]
let b = {a:1,b:[1,'9',3],c:false}
let c = 9
console.log(jsonStringfiy(a))
console.log(jsonStringfiy(b))
console.log(jsonStringfiy(c))