Superagent: Send JSON Object Alongside Files by Flatten the JSON Keys to HTML Form Names

sendAsHtmlForm.js

import request from 'superagent';

/*
 * given files is an array of File Objects: 
 * 
 * sendAsHtmlForm("/api/posts", 
 *   "post", {title: "a title", body. "a body"}, files)
 *
 */
function sendAsHtmlForm(url, method, json, files) {
  let theRequest = request.post(url)  
  // a hack for laravel 4.2 controllers
  // not recognizing form puts
  if (method == "put") {
    theRequest = theRequest.field('_method', 'put');
  }
  // add files
  files.forEach(
    (attachment, index) => theRequest.attach(`${index}`, attachment)
  );
  // flatten json to html form names
  toFormFields(entity.toJSON()).forEach(
    ([field, value]) => value ? theRequest.field(field, value) : null
  );
  return the_request.send();
};

function toFormFields(json, prefix = "") {
  if (
    Object.prototype.toString.call( json ) === '[object Array]'
  ) {
    return json.reduce(
      (all, elem, index) => all.concat(toFormFields(elem, prefix + `[${index}]`)), []
    )
  } else if (Object.prototype.toString.call( json ) === '[object Object]') {
    return Object.keys(json).reduce(
      (all, key) => all.concat(toFormFields(json[key], prefix ? prefix + `[${key}]` : `${key}`)), []
    );
  } else {
    return [[prefix, json]]
  }
};

module.exports(sendAsHtmlForm);