Set manipulation (javascript arrays) using lodash

Question

I'd like a more elegant and readable (if possible using functional programming style) for collection filtering (groupToAdd and groupToDelete collection handling)

Just getting rid of multiple _.findIndex() < 0 or _.indexOf() > -1 would make me happy

const {wrap} = require('co');
const _ = require('lodash');

function* manageUserOrganizations(userId, newOrgs, application, token, logger) {
    logger.debug('retrieving existing user groups');
    const userGroups = yield keycloak.getGroupsByUser(userId, token, logger);

    // determine groups operation to handle
    let groupToAdd;
    let groupToDelete;
    if (newOrgs && newOrgs.length) {
      // if some organizations to assign are provided add every one not already belonging to user
      groupToAdd = _.filter(application.subGroups, (elt) => _.findIndex(userGroups, {name: elt.name}) < 0);
      groupToAdd = _.filter(groupToAdd, (elt) => _.indexOf(newOrgs, elt.name) > -1);
      // and remove every one belonging to user but not provided  (including application itself)
      groupToDelete = _.filter(userGroups, (elt) => _.indexOf(newOrgs, elt.name) < 0);
    } else {
      // otherwise add the application itself except if it already belongs to user
      groupToAdd = _.findIndex(userGroups, {name: application.name}) > -1 ? [] : [application];
      // and remove all other existing groups
      groupToDelete = _.filter(userGroups, (elt) => elt.name !== application.name);
    }

    // handle user group assignation / removal
    yield Promise.all(_.flatten([
      groupToAdd
        .map(wrap(assignUserGroup(userId, token, logger.subProcess()))),
      groupToDelete
        .map(wrap(removeUserGroup(userId, token, logger.subProcess())))
    ]));
  }

organizations or applications are handled as groups in keycloak context

below are an example of variables values:

application.subGroups || userGroups: [{id: 665, name: 'orgName'}, {id: 667, name: 'newOrgName'}]

newOrgs: ['someOrgName', 'anotherOrgName']