Object to form data

objectToFormData.js

/**
 * 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 = '') => {
    for(let i = 0; i < _arr.length; i++) {
      if(Array.isArray(_arr[i])) {
        fromArray(_arr[i], getPrefix(prefix, i))
      }
      else if(_arr[i] instanceof Object && !(_arr[i] instanceof Blob)) {
        fromObject(_arr[i], getPrefix(prefix, i))
      } else {
        formData.append(getPrefix(prefix, _arr[i]), _arr[i])
      }
    }
  }

  const fromObject = (_obj, prefix = '') => {
    for(const [key, value] of Object.entries(_obj)) {
      if(Array.isArray(value)) {
        fromArray(value, getPrefix(prefix, key))
      } else if(value instanceof Object && !(value instanceof Blob)) {
        fromObject(value, getPrefix(prefix, key))
      } else {
        formData.append(getPrefix(prefix, key), value)
      }
    }
  }

  const formData = new FormData()

  fromObject(obj)

  return formData
}