Optimistic vendor inclusion. After all, YOU are writing the files inside /vendor. Upside: cleaner Context.js. Downside: not evident in Context if missing functions.

auth0.js

import Auth0 from 'npm-auth0';

export isAuthenticated() {

  // Access API with npm package
  // API returns this function's required return, so we return directly
  return Auth0.isAuthenticated();

}

Context.js

import zillow_functions from 'vendor/zillow';
import auth0_functions from 'vendor/auth0';
import packageJson from '../package.json';

export class Provider extends Component {
  
  state = {
    app_title = 'Houses',
    zip_code = 0,
    version = packageJson.version
  }
  
  functions = {

    // Assumes functions satisfy app requirements
    // You'll want to document these requirements
    ...zillow_functions,
    ...auth0_functions,
    
    // Then add functions unique to app
    update_zip_code = ( zip_code ) => {
      this.setState({ zip_code });
    }
    
  }
  
  render(){ return (
    <Context.Provider value={{
      ...this.state,
      ...this.functions
    }}>{ this.props.children }</Context.Provider>
  ); }

};

zillow.js

import Zillow from 'npm-zillow';

export get_house_from_address ( address ) {

  // Access API with npm package
  const house = Zillow.get_houses_from_zip( address );

  // Map to app's model
  return {
    bedrooms: house.bed_count,
    bathrooms: house.bath_count,
    isSold: house.status_sold,
  };

}