How to use the core-js/library/fn/object/assign function in core-js

constructor({
    el = null, value, maxItems = 10, itemTemplate = ITEM_TEMPLATE,
    geoLocate = true, apiRoot = 'https://api.teleport.org/api', apiVersion = 1,
    embeds = 'city:country,city:admin1_division,city:timezone/tz:offsets-now,city:urban_area',
  } = {}) {
    events(this);

    const elem = (typeof el === 'string') ? document.querySelector(el) : el;
    this.setupInput(elem);

    assign(this, {
      maxItems, geoLocate, apiRoot, apiVersion, itemTemplate, embeds, results: [],
      _activeIndex: 0, _cache: {}, _query: this.el.value, value,
    });

    // Prefetch results
    if (this.value && this.value.title) {
      this.query = this.value.title;
    } else if (this.query) {
      this.fetchResults(() => {
        this.value = this.getResultByTitle(this.query);
        this.emit('change', this.value);
      });
    }

    this.getCities = debounce(this.getCities, 200);
    return this;

refreshEvents: ['resize', 'karl:element#header:classToggled'],
  dropdownListClassName: 'k-PlatformSwitch k-PlatformSwitch--withoutBorderTop',
  dropdownContent: ,
  onToggle: function() {
    // Example event to trigger
    const event = document.createEvent('Event')
    event.initEvent('karl:platformSwitch:toggle', true, true)
    window.dispatchEvent(event)
  }
}

// Unlogged header dropdown
const unloggedPlatformSwitchProps = objectAssign(
  { positionedWith: () => document.getElementById('header') },
  platformSwitchProps
)
const KarlUnloggedHeaderPlatformSwitch = defaultProps(
  Dropdown,
  unloggedPlatformSwitchProps
)

// Logged header dropdowns
const loggedPlatformSwitchProps = objectAssign(
  { positionedWith: () => document.getElementById('header-logged') },
  platformSwitchProps
)
const KarlLoggedHeaderPlatformSwitch = defaultProps(
  Dropdown,
  loggedPlatformSwitchProps

import browserSync from 'browser-sync';

const bs = browserSync.create();
const gp = gulpLoadPlugins();


import pkg from './package.json';

const BANNER = `/*! ${pkg.name} - v${pkg.version} | ${pkg.homepage} | ${pkg.license} */
`;


// ----------------------------- BROWSERIFY ------------------------------------

// Browserify params
const browserifyArgs = assign({}, watchify.args, {
  standalone: 'TeleportAutocomplete',
  transform: [
    "babelify",
    ["ractivate", { "extensions": [".rac"] }]
  ],
  debug: true,
});

// Browserify bundle command
const rebundle = (bundler, entry) => {
  return bundler.bundle()
    .on('error', gp.util.log)
    .pipe(source(entry))
    .pipe(gp.derequire())
    .pipe(buffer())
    .pipe(gp.rename({

window.dispatchEvent(event)
  }
}

// Unlogged header dropdown
const unloggedPlatformSwitchProps = objectAssign(
  { positionedWith: () => document.getElementById('header') },
  platformSwitchProps
)
const KarlUnloggedHeaderPlatformSwitch = defaultProps(
  Dropdown,
  unloggedPlatformSwitchProps
)

// Logged header dropdowns
const loggedPlatformSwitchProps = objectAssign(
  { positionedWith: () => document.getElementById('header-logged') },
  platformSwitchProps
)
const KarlLoggedHeaderPlatformSwitch = defaultProps(
  Dropdown,
  loggedPlatformSwitchProps
)

const userMenuDropdownList = [
  <a href="#">Mon profil</a>,
  <a href="#">Mes projets</a>,
  <a href="#">Mes contributions</a>,
  <a href="#">Mes messages</a>,

static init(el, options = {}) {
    const opt = (typeof el === 'string' || el instanceof HTMLInputElement) ? assign(options, { el }) : el;
    return new TeleportAutocomplete(opt);
  }

onrender() {
    const { maxItems, apiRoot, geoLocate, itemTemplate, embeds, value } = this.get();

    this.ac = new Autocomplete(assign({ el: this.find('input') }, {
      maxItems, apiRoot, geoLocate, itemTemplate, embeds, value,
    }));

    this.ac.on('change', val => this.set('value', val));
    this.ac.on('querychange', query => this.set('query', query));
  },

parseCity(res) {
    const city = res.embedded('location:nearest-city') || res.embedded('city:item');
    city.country = city.embedded('city:country');
    city.admin1_division = city.embedded('city:admin1_division');
    city.timezone = city.embedded('city:timezone');
    city.urban_area = city.embedded('city:urban_area');

    const { full_name: fullName, name, geoname_id: geonameId, population,
      location: { latlon: { latitude, longitude } } } = city;

    const { matching_full_name: title = fullName } = res;

    const result = { title, name, geonameId, latitude, longitude, population };

    if (city.country) assign(result, { country: city.country.name });
    if (city.admin1_division) {
      const { name: admin1Division, geonames_admin1_code: admin1DivisionCode } = city.admin1_division;
      assign(result, { admin1Division, admin1DivisionCode });
    }

    if (city.timezone) {
      const tzNow = city.timezone.embedded('tz:offsets-now');
      assign(result, { tzOffsetMinutes: tzNow.total_offset_min });
    }

    if (city.urban_area) {
      const { slug: uaSlug, name: uaName, ua_id: uaId, teleport_city_url: uaCityUrl } = city.urban_area;
      assign(result, { uaName, uaId, uaCityUrl, uaSlug });
    }

    return result;

city.country = city.embedded('city:country');
    city.admin1_division = city.embedded('city:admin1_division');
    city.timezone = city.embedded('city:timezone');
    city.urban_area = city.embedded('city:urban_area');

    const { full_name: fullName, name, geoname_id: geonameId, population,
      location: { latlon: { latitude, longitude } } } = city;

    const { matching_full_name: title = fullName } = res;

    const result = { title, name, geonameId, latitude, longitude, population };

    if (city.country) assign(result, { country: city.country.name });
    if (city.admin1_division) {
      const { name: admin1Division, geonames_admin1_code: admin1DivisionCode } = city.admin1_division;
      assign(result, { admin1Division, admin1DivisionCode });
    }

    if (city.timezone) {
      const tzNow = city.timezone.embedded('tz:offsets-now');
      assign(result, { tzOffsetMinutes: tzNow.total_offset_min });
    }

    if (city.urban_area) {
      const { slug: uaSlug, name: uaName, ua_id: uaId, teleport_city_url: uaCityUrl } = city.urban_area;
      assign(result, { uaName, uaId, uaCityUrl, uaSlug });
    }

    return result;
  }
}

const tasks = ['js/autocomplete.js', 'js/autocomplete-ractive.js'].map(entry => {
    const bundler = watchify(browserify(assign(browserifyArgs, { entries: [entry] })));

    bundler.on('update', rebundle.bind(this, bundler, entry));
    bundler.on('log', gp.util.log);

    return rebundle(bundler, entry);
  });