serializeForm.js

function update(data, keys, value) {
  if (keys.length === 0) {
    return value
  }

  let key = keys.shift()

  if (!key) {
    data = data || {}
    if (Array.isArray(data)) {
      key = data.length
    }
  }

  let index = +key

  if (!isNaN(index)) {
    data = data || {}
    key = index
  }

  data = data || {}
  let val = update(data[key], keys, value)
  data[key] = val

  return data
}

const serializeForm = (formData) => {

  const filteredEmpty = Array.from(formData.entries()).filter(function ([field, value]) {
    return value !== "";
  });

  return filteredEmpty.reduce((data, [field, value]) => {

    let [_, prefix, keys] = field.match(/^([^\[]+)((?:\[[^\]]*\])*)/)

    if (keys) {
      keys = Array.from(keys.matchAll(/\[([^\]]*)\]/g), m => m[1])
      value = update(data[prefix], keys, value)
    }

    data[prefix] = value

    return data
  }, {})
}

export default serializeForm