SOURCE

/* 
作者：德布罗煜
链接：https://www.nowcoder.com/discuss/860063?type=post&order=create&pos=&page=1&ncTraceId=&channel=-1&source_id=search_post_nctrack&subType=2&gio_id=4B11D26016AC8D56CAC57B6E316F3069-1646982291847
来源：牛客网

{
    a: 'a',
    b: [1, { c: true }, [3]],
    d: { e: undefined, f: 3 },
    g: null,
}
输入用例记不太清了，应该大致差不多吧

输出：

{
    a: "a",
    b[0]: 1,
    b[1].c: true,
    b[2][0]: 3,
    d.f: 3
    // null和undefined直接舍去
}

*/

const flat = (obj) => {
    const ret = {}
    for(let [key, value] of Object.entries(obj)) {
        // 如果value是数组
        if (typeof value === 'object' && value !== null) {
            const temp = flat(value)
            for (let [innerKey, innerVal] of Object.entries(temp)) {
                if (!/^\d/.test(key) && !innerKey.startsWith('[')) {
                    ret[`${key}.${innerKey}`] = innerVal
                } else if (/^\d/.test(key)) {
                    ret[`[${key}].${innerKey}`] = innerVal
                } else {
                    ret[`${key}${innerKey}`] = innerVal
                }   
            }
        } 
         else if (value !== null && value !== undefined) {
            if (/^\d/.test(key)) {
                ret[`[${key}]`] = value
            } else {
                ret[key] = value
            }       
        }
    }
    return ret
}
console.log(flat(({a:'a', b: [1,2], c:{d:3, g: undefined, h:[1,2,{k:'k', g: [1,2,3]}]}, e: null, f:undefined})))