phgrund

const objectAssignNotNull = (target, ...sources) => {
  for (const source of sources) {
    for (const [key, value] of Object.entries(source)) {
      if (value && typeof value === 'object' && !Array.isArray(value)) {
        if (!target[key]) target[key] = {}
        objectAssignNotNull(target[key], value)
      } else if ((value !== null && value !== undefined) || !Object.prototype.hasOwnProperty.call(target, key)) {
        Object.assign(target, { [key]: value })
      }
    }

phgrund

/**
 * Append every property of an object into a formData, then returns it.
 *
 * @param  {Object}   obj     Original object.
 * @return {FormData}         FormData object reference.
 */
function objectToFormData(obj) {
  const getPrefix = (prefix, key) => prefix + (prefix ? '[' : '') + key + (prefix ? ']' : '')

  const fromArray = (_arr, prefix = '') => {