objectToFormData.js

const isObject = value => value === Object(value)
const isArray = value => Array.isArray(value)
const isFile = value => value instanceof File
const makeArrayKey = (key) => {
	if (key.length > 2 && key.lastIndexOf('[]') === key.length - 2) {
		return key
	} else {
		return key + '[]'
	}
}

const objectToFormData = function objectToFormData(obj, fd, pre) {
	let formData = fd || new FormData()

	if (obj === undefined || obj === null) {
		return
	}

	Object.keys(obj).forEach(function (prop) {
		const key = pre ? (pre + '[' + prop + ']') : prop

		if (isObject(obj[prop]) && !isArray(obj[prop]) && !isFile(obj[prop])) {
			objectToFormData(obj[prop], formData, key)
		} else if (isArray(obj[prop])) {
			obj[prop].forEach(function (value) {
				const arrayKey = makeArrayKey(key)

				if (isObject(value) && !isFile(value)) {
					objectToFormData(value, formData, arrayKey)
				} else {
					formData.append(arrayKey, value)
				}
			})
		} else {
			formData.append(key, obj[prop])
		}
	})

	return formData
}

export default objectToFormData