SOURCE

const input = {
    a: 1,
    b: [1, 2, {c: true}, [3]],
    d: {e: 2, f: 3},
    g: null
}
const output = {
    "a": 1,
    "b[0]": 1,
    "b[1]": 2,
    "b[2].c": true,
    "b[3][0]": 3,
    "d.e": 2,
    "d.f": 3
}
function getType (param) {
    const match = Object.prototype.toString.call(param).match(/\[object (\w+)\]/)
    return match ? match[1] : ''
}
function isvalidVal (val) {
    return val !== undefined && val !== null
}
function getNameByRootType (baseKey, key, type) {
    if (baseKey == '') return key
    if (type == 'Object') {
        return `${baseKey}.${key}`
    } else if (type == 'Array') {
        return `${baseKey}[${key}]`
    } else {
        return baseKey + key
    }
}
// 处理 Object、Array
const flatten = (input, result, baseK = '') => {
    const rootTpye = getType(input)
    for (const [key, val] of Object.entries(input)) {
        if (isvalidVal(val)) {
            const keyName = getNameByRootType(baseK, key, rootTpye)
            if (typeof val == 'object') {
                flatten(val, result, keyName)
            } else {
                result[keyName] = val
            }
        }
    }
}
const result = {}
flatten(input, result)
console.log(result)