src/Formio.js

import { Formio } from '@formio/core';
import CDN from './CDN';
import Providers from './providers';
Formio.cdn = new CDN();
Formio.Providers = Providers;
Formio.version = 'FORMIO_VERSION';

const isNil = (val) => val === null || val === undefined;
Formio.prototype.uploadFile = function(storage, file, fileName, dir, progressCallback, url, options, fileKey, groupPermissions, groupId, uploadStartCallback, abortCallback) {
  const requestArgs = {
    provider: storage,
    method: 'upload',
    file: file,
    fileName: fileName,
    dir: dir
  };
  fileKey = fileKey || 'file';
  const request = Formio.pluginWait('preRequest', requestArgs)
    .then(() => {
      return Formio.pluginGet('fileRequest', requestArgs)
        .then((result) => {
          if (storage && isNil(result)) {
            const Provider = Providers.getProvider('storage', storage);
            if (Provider) {
              const provider = new Provider(this);
              if (uploadStartCallback) {
                uploadStartCallback();
              }
              return provider.uploadFile(file, fileName, dir, progressCallback, url, options, fileKey, groupPermissions, groupId, abortCallback);
            }
            else {
              throw ('Storage provider not found');
            }
          }
          return result || { url: '' };
        });
    });

  return Formio.pluginAlter('wrapFileRequestPromise', request, requestArgs);
};

Formio.prototype.downloadFile = function(file, options) {
  const requestArgs = {
    method: 'download',
    file: file
  };

  const request = Formio.pluginWait('preRequest', requestArgs)
    .then(() => {
      return Formio.pluginGet('fileRequest', requestArgs)
        .then((result) => {
          if (file.storage && isNil(result)) {
            const Provider = Providers.getProvider('storage', file.storage);
            if (Provider) {
              const provider = new Provider(this);
              return provider.downloadFile(file, options);
            }
            else {
              throw ('Storage provider not found');
            }
          }
          return result || { url: '' };
        });
    });

  return Formio.pluginAlter('wrapFileRequestPromise', request, requestArgs);
};

Formio.prototype.deleteFile = function(file, options) {
  const requestArgs = {
    method: 'delete',
    file: file
  };

  const request = Formio.pluginWait('preRequest', requestArgs)
    .then(() => {
      return Formio.pluginGet('fileRequest', requestArgs)
        .then((result) => {
          if (file.storage && isNil(result)) {
            const Provider = Providers.getProvider('storage', file.storage);
            if (Provider) {
              const provider = new Provider(this);
              return provider.deleteFile(file, options);
            }
            else {
              throw ('Storage provider not found');
            }
          }
          return result || { url: '' };
        });
    });

  return Formio.pluginAlter('wrapFileRequestPromise', request, requestArgs);
};

// For reverse compatability.
Formio.Promise = Promise;
export { Formio };