myflatten-optimize.js

var data = {
    header: {
        "x-request-id": "1"
    },
    "body": {
        "guid": "1234",
        "items": [
            {
                "name": "item1",
                "quantity": {"num": [{value: 100, data: "A"}, {value: 101, data: "A1"}], "numStr": "hundread"}
            },
            {
                "name": "item2",
                "quantity": {"num": [{value: 200, data: "B"}, {value: 201, data: "B1"}], "numStr": "two hundread"}
            }
        ]
    }
}

function myFlatten(target, opt = {}) {
    const delimiter = '.'
    const output = {}
    if (opt.allKey){
        output[opt.allKey] = []
    }

    function step(object, prev, hasArray) {
        const rootType = Object.prototype.toString.call(object)
        const rootIsArray = (rootType === '[object Array]')
        Object.keys(object).forEach(function (key) {
            const value = object[key]
            const type = Object.prototype.toString.call(value)
            const isObject = (type === '[object Object]')
            const isArray = (type === '[object Array]')
            let newKey = opt.arrayFlatten && rootIsArray ? "" : delimiter + key
            newKey = prev ? prev + newKey : key
            if ((isObject || isArray) && Object.keys(value).length) {
                return step(value, newKey, hasArray || rootIsArray || isArray)
            }
            const strValue = value.toString()
            opt.allKey && output[opt.allKey].push(strValue)
            if (opt.arrayFlatten && hasArray) {
                if (!output.hasOwnProperty(newKey)) {
                    output[newKey] = []
                }
                output[newKey].push(strValue)
            } else {
                output[newKey] = strValue
            }
        })
    }
    step(target)
    return output
}

console.log(myFlatten(data, {allKey : "all", arrayFlatten : false}));
/*
{
  all: [
    '1',     '1234',
    'item1', '100',
    'A',     '101',
    'A1',    'hundread',
    'item2', '200',
    'B',     '201',
    'B1',    'two hundread'
  ],
  'header.x-request-id': '1',
  'body.guid': '1234',
  'body.items.0.name': 'item1',
  'body.items.0.quantity.num.0.value': '100',
  'body.items.0.quantity.num.0.data': 'A',
  'body.items.0.quantity.num.1.value': '101',
  'body.items.0.quantity.num.1.data': 'A1',
  'body.items.0.quantity.numStr': 'hundread',
  'body.items.1.name': 'item2',
  'body.items.1.quantity.num.0.value': '200',
  'body.items.1.quantity.num.0.data': 'B',
  'body.items.1.quantity.num.1.value': '201',
  'body.items.1.quantity.num.1.data': 'B1',
  'body.items.1.quantity.numStr': 'two hundread'
}
*/

console.log(myFlatten(data, {allKey : "all", arrayFlatten : true}));

/*
{
  all: [
    '1',     '1234',
    'item1', '100',
    'A',     '101',
    'A1',    'hundread',
    'item2', '200',
    'B',     '201',
    'B1',    'two hundread'
  ],
  'header.x-request-id': '1',
  'body.guid': '1234',
  'body.items.name': [ 'item1', 'item2' ],
  'body.items.quantity.num.value': [ '100', '101', '200', '201' ],
  'body.items.quantity.num.data': [ 'A', 'A1', 'B', 'B1' ],
  'body.items.quantity.numStr': [ 'hundread', 'two hundread' ]
}
*/

기본 구조는 아래 라이브러리의 flatten 을 참고했음
https://github.com/hughsk/flat/blob/master/index.js