text: /* *******************************************************************************************
   * FEATHERS.JS CHEATSHEET
   * https://docs.feathersjs.com/api/readme.html
   * 
   * 1. CORE: Feathers core functionality.
   * 2. TRANSPORT: Expose a Feathers application as an API server.
   * 3. CLIENT: More details on how to use Feathers on the client.
   * 4. AUTHENTICATION: Feathers authentication mechanism.
   * 5. DATABASE: Feathers common database adapter API and querying mechanism.
   * ******************************************************************************************* */
  
  
  /* *******************************************************************************************
   * 1. CORE: Feathers core functionality.
   * ******************************************************************************************* */
  
  
  ```
  # Provides the ability to initialize new application instances
  npm install @feathersjs/feathers --save
  
  # Provides a set of standard error classes used by all other Feathers modules
  npm install @feathersjs/errors --save
  ```
  
  // --> APPLICATION <--
  // https://docs.feathersjs.com/api/application.html
  
  const feathers = require('@feathersjs/feathers');
  
  const app = feathers();                      // application initialization
  
  app.mixins                                   // contains a list of service mixins
  
  app.use(path, service)                       // allows registering a service object on a given path
  app.service(path)                            // returns the wrapped service object for the given path
  app.hooks(hooks)                             // allows registration of application-level hooks
  app.publish([event,], publisher)             // registers a global event publisher
  app.configure(callback)                      // runs a callback function that gets passed the application object
  app.listen(port)                             // starts the application on the given port
  app.setup([server])                          // used to initialize all services by calling each services .setup(app, path) method (if available)
  app.set(name, value)                         // assigns setting name to value
  app.get(name)                                // retrieves the setting name
  app.on(eventname, listener)                  // registers a listener method for the given eventname
  app.emit(eventname, data)                    // emits the event eventname to all event listeners
  app.removeListener(eventname, [ listener ])  // removes all or the given listener for eventname
  
  // --> SERVICES <--
  // https://docs.feathersjs.com/api/services.html
  
  // "Services" are the heart of every Feathers application.
  // Services are JavaScript objects (or instances of ES6 classes) that implement certain methods.
  // Feathers itself will also add some additional methods and functionality to its services.
  class MyService {
    // Retrieves a list of all resources from the service.
    // Provider parameters will be passed as params.query.
    async find(params) {
      return [];
    }
  
    // Retrieves a single resource with the given id from the service.
    async get(id, params) {}
  
    // Creates a new resource with data.
    // The method should return the newly created data. data may also be an array.
    async create(data, params) {}
  
    // Replaces the resource identified by id with data.
    // The method should return the complete, updated resource data.
    // id can also be null when updating multiple records, with params.query containing the query criteria.
    async update(id, data, params) {}
  
    // Merges the existing data of the resource identified by id with the new data.
    // id can also be null indicating that multiple resources should be patched with params.query containing the query criteria.
    async patch(id, data, params) {}
  
    // Removes the resource with id.
    // The method should return the removed resource.
    // id can also be null, which indicates the deletion of multiple resources, with params.query containing the query criteria.
    async remove(id, params) {}
  
    // A special method that initializes the service, passing an instance of the Feathers application
    // and the path it has been registered on.
    // For services registered before app.listen is invoked, the setup function of each registered service
    // is called on invoking app.listen. For services registered after app.listen is invoked, setup is
    // called automatically by Feathers when a service is registered.
    setup(app, path) {}
  }
  
  params.query     // contains the URL query parameters sent from the client
  params.provider  // for any service method call made through REST params.provider will be set to rest
  
  app.use('/my-service', new MyService());
  
  // Important: Always use the service returned by app.service(path)
  const myService = app.service('my-service');
  
  myService.hooks(hooks)                             // register hooks for this service
  myService.publish([event,], publisher)             // register an event publishing callback
  myService.mixin(mixin)                             // extends the functionality of a service
  myService.on(eventname, listener)                  // registers a listener method for the given eventname
  myService.once(eventname, listener)                // registers a listener method for the given eventname that will be triggered only one time
  myService.emit(eventname, data)                    // emits the event eventname to all event listeners
  myService.removeListener(eventname, [ listener ])  // removes all listeners (or the given listener) for eventname
  
  // --> HOOKS <--
  // https://docs.feathersjs.com/api/hooks.html
  
  // Hooks are pluggable middleware functions that can be registered
  // before, after or on errors of a service method. You can register a
  // single hook function or create a chain of them to create complex work-flows.
  app.service('my-service').hooks({
    before: {
      all: [
        // Use normal functions
        async function(context) { console.log('before all hook ran'); }
      ],
  
      find: [
        // Use ES6 arrow functions
        context => console.log('before find hook 1 ran'),
        async context => console.log('before find hook 2 ran')
      ],
  
      async create (context) {
        return context
      },
    },
  
    after: {
      all: [],
      find: [],
      get: [],
      create: [],
      update: [],
      patch: [],
      remove: []
    },
  
    // Here is an example for a very useful application hook that logs every service method error
    // with the service and method name as well as the error stack
    error(context) {
      console.error(`Error in ${context.path} calling ${context.method} method`, context.error);
    }
  });
  
  context.app       // [read only] contains the Feathers application object
  context.service   // [read only] contains the service this hook currently runs on
  context.path      // [read only] contains the service name (or path) without leading or trailing slashes
  context.method    // [read only] contains the name of the service method (find, get, create, update...)
  context.type      // [read only] contains the hook type (one of before, after or error)
  context.params    // [writable] contains the service method parameters (including params.query)
  context.id        // [writable] contains the id for a get, remove, update and patch service method call
  context.data      // [writable] contains the data of a create, update and patch service method call
  context.error     // [writable] contains the error object that was thrown in a failed method call (only available in error hooks)
  context.result    // [writable] contains the result of the successful service method call (only available in after hooks)
  context.dispatch  // [writable and optional] contains a "safe" version of the data that should be sent to any client
  
  // --> CHANNELS <--
  // https://docs.feathersjs.com/api/channels.html
  
  // A channel is an object that contains a number of connections.
  // It can be created via app.channel and allows a connection to join or leave it.
  app.channel(name)                     // when given a single name, returns an existing or new named channel
  app.channel(name1, name2, ... nameN)  // when given multiples names, will return a combined channel.
  app.channels                          // returns a list of all existing channel names
  
  channel.join(connection)      // adds a connection to this channel
  channel.leave(connection|fn)  // removes a connection from this channel
  channel.filter(fn)            // returns a new channel filtered by a given function which gets passed the connection
  channel.send(data)            // returns a copy of this channel with customized data that should be sent for this event
  
  channel.connections  // contains a list of all connections in this channel
  channel.length       // returns the total number of connections in this channel
  
  service.publish([event,] fn)  // registers a publishing function for a specific service for a specific event or all events if no event name was given
  app.publish([event,] fn)      // registers an event publishing callback
  
  app.on('connection', connection => {})  // fired every time a new real-time connection is established
  app.on('disconnection', connection => {})
  app.on('login', (authenticationResult, params, context) => {})  // sent by the authentication module and also contains the connection in the info object that is passed as the second parameter
  
  
  /* *******************************************************************************************
   * 2. TRANSPORT: Expose a Feathers application as an API server.
   * ******************************************************************************************* */
  
  
  ```
  # Contains Express framework integrations
  npm install @feathersjs/express --save
  
  # Allows to call service methods and receive real-time events
  npm install @feathersjs/socketio --save
  
  # Allows to call service methods and receive real-time events via Primus
  npm install @feathersjs/primus --save
  ```
  
  // --> EXPRESS <--
  // https://docs.feathersjs.com/api/express.html
  
  const feathers = require('@feathersjs/feathers');
  const express = require('@feathersjs/express');
  
  // Create an app that is a Feathers AND Express application
  const app = express(feathers());
  
  // If no Feathers application is passed, express() returns a plain Express application
  // just like a normal call to Express would
  const app = express();
  
  app.use(path, service|mw)        // registers either a service object or an Express middleware on the given path
  app.listen(port)                 // will first call Express app.listen and then internally also call the Feathers app.setup(server)
  app.setup(server)                // usually called internally by app.listen but in the cases described below needs to be called explicitly
  
  express.rest()                   // registers a Feathers transport mechanism that allows you to expose and consume services through a RESTful API.
  app.configure(express.rest())    // configures the transport provider with a standard formatter sending JSON response via res.json
  
  express.notFound()               // returns middleware that returns a NotFound (404) Feathers error
  express.errorHandler()           // middleware that formats any error response to a REST call as JSON and sets the appropriate error code
  app.use(express.errorHandler())  // set up the error handler with the default configuration
  
  // --> SOCKET.IO <--
  // https://docs.feathersjs.com/api/client/socketio.html
  
  const feathers = require('@feathersjs/feathers');
  const socketio = require('@feathersjs/socketio');
  
  const app = feathers();
  
  app.configure(socketio());                            // sets up the Socket.io transport with the default configuration using either the server provided by app.listen or passed in app.setup(server)
  app.configure(socketio(callback))                     // sets up the Socket.io transport with the default configuration and call callback with the Socket.io server object
  app.configure(socketio(options [, callback]))         // sets up the Socket.io transport with the given Socket.io options object and optionally calls the callback
  app.configure(socketio(port, [options], [callback]))  // creates a new Socket.io server on a separate port. Options and a callback are optional
  
  // --> PRIMUS <--
  // https://docs.feathersjs.com/api/client/primus.html
  
  app.configure(primus(options))            // sets up the Primus transport with the given Primus options
  app.configure(primus(options, callback))  // sets up the Primus transport with the given Primus options and calls the callback with the Primus server instance
  
  
  /* *******************************************************************************************
   * 3. CLIENT: More details on how to use Feathers on the client.
   * ******************************************************************************************* */
  
  
  ```
  # Bundles the separate Feathers client side modules into one providing the code as ES5 (compatible with modern browsers)
  # You do not have to install or load any of the other modules listed below
  npm install @feathersjs/client --save
  
  # Allows to connect to services through REST HTTP
  npm install @feathersjs/rest-client --save
  
  # Allows to connect to services through Socket.io
  npm install @feathersjs/socketio-client --save
  
  # Allows to connect to services through Primus
  npm install @feathersjs/primus-client --save
  
  # Allows you to easily authenticate against a Feathers server
  npm install @feathersjs/authentication-client --save
  ```
  
  // --> REST CLIENT <--
  // https://docs.feathersjs.com/api/client/rest.html
  
  rest([baseUrl])  // Initialize a client object with a base URL
  
  app.configure(restClient.jquery(window.jQuery));   // connect to a service using jQuery
  app.configure(restClient.request(requestClient));  // connect to a service using request
  app.configure(restClient.superagent(superagent));  // connect to a service using Superagent
  app.configure(restClient.axios(axios));            // connect to a service using Axios
  app.configure(restClient.fetch(window.fetch));     // connect to a service using Fetch
  
  // --> SOCKET.IO <--
  // https://docs.feathersjs.com/api/client/socketio.html
  
  socketio(socket)           // initialize the Socket.io client using a given socket and the default options
  socketio(socket, options)  // initialize the Socket.io client using a given socket and the given options
  
  // --> PRIMUS <--
  // https://docs.feathersjs.com/api/client/primus.html
  
  primus(socket)           // initialize the Primus client using a given socket and the default options
  primus(socket, options)  // initialize the Primus client using a given socket and the given options
  
  
  /* *******************************************************************************************
   * 4. AUTHENTICATION: Feathers authentication mechanism.
   * ******************************************************************************************* */
  
  
  ```
  # Assists in using JWT for authentication
  npm install @feathersjs/authentication --save
  
  # Wraps the passport-local authentication strategy (username and password)
  npm install @feathersjs/authentication-local --save
  
  # Allows to use 180+ oAuth providers (Facebook, Google, Twitter etc.)
  npm install @feathersjs/authentication-oauth --save
  ```
  
  // --> SERVER <--
  // https://docs.feathersjs.com/api/authentication/server.html
  
  const options = {
    "authentication": {
      "secret": "CHANGE_ME", // The token signing secret
      "entity": "user", // the entity that will be added to the request, socket, and context.params. (ie. req.user, socket.user, context.params.user)
      "service": "users", // the service to look up the entity
      "authStrategies": [ "jwt", "local" ], // The authentication strategies to allow to create a token
      "jwtOptions": {
        "header": { "typ": "access" }, // by default is an access token but can be any type
        "audience": "https://yourdomain.com", // The resource server where the token is processed
        "issuer": "feathers", // The issuing server, application or resource
        "algorithm": "HS256", // the algorithm to use
        "expiresIn": "1d" // the access token expiry
      }
    }
  }
  
  const { AuthenticationService, JWTStrategy } = require('@feathersjs/authentication');
  
  let authService = new AuthenticationService(app);
  
  service.register('jwt', new JWTStrategy());
  
  app.use('/authentication', authService);
  app.configure(expressOauth());
  
  app.get('defaultAuthentication') // The name of the default authentication service
  
  authService = app.service('authentication')  // service for creating JWT (implements only the create and remove methods)
  
  authService.hooks({ before })  // registers hooks for this service
  authService.hooks({ after })   // registers hooks for this service
  
  new AuthenticationService(app) // Create a new authentication service
  
  class MyAuthenticationService extends AuthenticationService {} // Customize the authentication service
  
  authService.authenticate(data, params, ...strategies) // Authenticate with strategies
  authService.create(data, params) // Authenticate with data and params
  authService.create({ // Authenticate and create a JWT using the local strategy email/password
    strategy: 'local',
    email: 'hello@feathersjs.com',
    password: 'supersecret'
  });
  authService.remove(id, params) // removes the JWT token (mostly exists for the logout process)
  authService.configuration // The current configuration
  authService.register(name, strategy) // Register a new authentication strategy
  authService.createAccessToken(payload) // Create a new access token with payload
  authService.verifyAccessToken(accessToken) // Verify an existing access token
  authService.getTokenOptions(authResult, params) // Get the options for a token
  authService.getPayload(authResult, params) // Return the payload for an authentication result
  authService.parse(req, res, ...strategies) // Parse an HTTP request and response with using a list of strategies
  
  
  app.on('login', callback))   // emits an event whenever a client successfully authenticates
  app.on('logout', callback))  // emits an event whenever a client successfully logout
  
  // --> CLIENT <--
  // https://docs.feathersjs.com/api/authentication/client.html
  
  const options = {
    storage: window.localStorage, // The storage to store the access token
    path: '/authentication', // The path of the authentication service
    locationKey: 'access_token', // The name of the window hash parameter to parse for an access token from the window.location. Usually used by the oAuth flow.
    locationErrorKey: 'error', // The name of the window hash parameter to parse for authentication errors. Usually used by the oAuth flow.
    jwtStrategy: 'jwt', // The access token authentication strategy
    storageKey: 'feathers-jwt', // Key for storing the token in e.g. localStorage
    header: 'Authorization', // Name of the accessToken header
    scheme: 'Bearer', // The HTTP header scheme
    Authentication: AuthenticationClient // Allows to provide a customized authentication client class
  }
  
  app.configure(auth(options))  // configure the authentication plugin with the given options
  
  app.reAuthenticate()        // authenticates using the JWT from the storage
  app.authenticate(options)  // authenticate with a Feathers server by passing a strategy and other properties as credentials
  app.logout()               // removes the JWT accessToken from storage on the client
  
  const authenticationInfo = await app.get('authentication'); // The authenticatoin information (like the user)
  
  app.on('login', callback)  // emits an event whenever the client successfully authenticates
  app.on('logout', callback) // emits an event whenever the client successfully authenticates
  
  // --> LOCAL (EMAIL & PASSWORD) <--
  // https://docs.feathersjs.com/api/authentication/local.html
  
  const { LocalStrategy } = require('@feathersjs/authentication-local');
  
  const options = {
    usernameField: 'email', // Name of the username field in the (e.g. 'email')
    passwordField: 'password', // Name of the password field (e.g. 'password')
    hashSize: 10, // The BCrypt hash size
    errorMessage: 'Invalid login', // The error message to return on errors
    entityUsernameField: usernameField, // Name of the username field on the entity if authentication request data and entity field names are different
    entityPasswordField: passwordField // Name of the password field on the entity if authentication request data and entity field names are different
  }
  
  authService.register('local', new LocalStrategy());
  
  local.hooks.hashPassword()       // hashes plain text passwords before they are saved to the database
  local.hooks.protect('password')  // makes sure that protected fields don't get sent to a client
  
  // --> OAUTH <--
  // https://docs.feathersjs.com/api/authentication/oauth.html
  const { expressOauth, OAuthStrategy } = require('@feathersjs/authentication-oauth');
  
  class GitHubStrategy extends OAuthStrategy {
    async getEntityData(profile) {
      const baseData = await super.getEntityData(profile);
  
      return {
        ...baseData,
        email: profile.email
      };
    }
  }
  
  authService.register('github', new MyGitHubStrategy());
  
  const options = {
    authentication: {
      oauth: {
        redirect: '/', // The redirect after a successful login
        github: { // The per-strategy configuration
          key: '<Client ID>',
          secret: '<Client secret>'
        }
      }
    }
  }
  
  app.configure(expressOauth(options));
  
  
  /* *******************************************************************************************
   * 5. DATABASE: Feathers common database adapter API and querying mechanism.
   * ******************************************************************************************* */
  
  
  ```
  # [MEMORY/FILESYSTEM] In-memory database adapter
  npm install feathers-memory --save
  
  # [MEMORY/FILESYSTEM] Database adapter for NeDB an in-memory or file system based standalone database
  npm install feathers-nedb --save
  
  # [MEMORY/FILESYSTEM] Adapter for Client side Feathers that can use the browsers LocalStorage or ReactNative's AsyncStorage
  npm install feathers-localstorage --save
  
  # [SQL] Adapter for KnexJS, an SQL query builder for NodeJS supporting PostgreSQL, MySQL, SQLite and MSSQL
  npm install feathers-knex --save
  
  # [SQL] Adapter for Sequelize an ORM for NodeJS supporting PostgreSQL, MySQL, SQLite and MSSQL
  npm install feathers-sequelize --save
  
  # [NOSSQL] Database adapter for MongoDB using the official NodeJS database driver
  npm install feathers-mongodb --save
  
  # [NOSSQL] Database adapter for Mongoose an Object Modelling library for NodeJS and MongoDB
  npm install feathers-mongoose --save
  
  # [NOSSQL] Database adapter for Elasticsearch
  npm install feathers-elasticsearch --save
  
  # [NOSSQL] Database adapter for RethinkDB a real-time database.
  npm install feathers-rethinkdb --save
  ```
  
  // --> COMMON API <--
  // https://docs.feathersjs.com/api/databases/common.html
  
  const service = require('feathers-<adaptername>');
  
  app.use('/messages', service({
    id: undefined,         // (optional) name of the id field property (usually set by default to id or _id)
    events: undefined,     // (optional) list of custom service events sent by this service
    paginate: {            // (optional) a pagination object containing a default and max page size
      default: undefined,  // sets the default number of items when $limit is not set
      max: undefined       // sets the maximum allowed number of items per page (even if the $limit query parameter is set higher)
    },
    whitelist: [],          // A list of additional non-standard query parameters to allow (e.g [ '$regex', '$populate' ])
    multi: true             // Allow create with arrays and update and remove with id null to change multiple items
  }));
  
  adapter.find()                    // returns a list of all records matching the query in params.query using the common querying mechanism
  adapter.get(id, params)           // retrieves a single record by its unique identifier (the field set in the id option during initialization)
  adapter.create(data, params)      // creates a new record with data. data can also be an array to create multiple records
  adapter.update(id, data, params)  // completely replaces a single record identified by id with data. Does not allow replacing multiple records (id can't be null). id can not be changed.
  adapter.patch(id, data, params)   // merges a record identified by id with data. id can be null to allow replacing multiple records (all records that match params.query the same as in .find). id can not be changed
  adapter.remove(id, params)        // removes a record identified by id. id can be null to allow removing multiple records (all records that match params.query the same as in .find)
  
  // Hook-less
  adapter._find()
  adapter._get(id, params)
  adapter._create(data, params)
  adapter._update(id, data, params)
  adapter._patch(id, data, params)
  adapter._remove(id, params)
  
  // --> QUERYING <--
  // https://docs.feathersjs.com/api/databases/querying.html
  
  app.service('messages').find({
    query: {
      $limit: 2,                      // will return only the number of results you specify
      $select: [ 'text', 'userId' ],  // allows to pick which fields to include in the result
      $skip: 2,                       // will skip the specified number of results
      $sort: {                        // will sort based on the object you provide. It can contain a list of properties by which to sort mapped to the order
        createdAt: -1
      },
      $or: [                          // find all records that match any of the given criteria
        { archived: { $ne: true } },
        { roomId: 2 }
      ],
      read: false,                    // compared directly for equality
      roomId: {
        $in: [ 2, 5 ],                // find all records where the property does match any of the given values
        $nin: [ 1, 3 ]                // find all records where the property does not match any of the given values
      },
      createdAt: {
        $lt: new Date().getTime(),    // find all records where the value is less to a given value
        $lte: new Date().getTime(),   // find all records where the value is less and equal to a given value
        $gt: new Date().getTime(),    // find all records where the value is more to a given value
        $gte: new Date().getTime(),   // find all records where the value is more and equal to a given value
      },
      archived: {
        $ne: true                     // find all records that do not equal the given property value
      }
    }
  });
  
  // With pagination enabled, to just get the number of available records set $limit to 0.
  // This will only run a (fast) counting query against the database and return a page object with
  // the total and an empty data array.
  
  
  /* *******************************************************************************************
   * 5. APPLICATION ARCHITECTURE
   * ******************************************************************************************* */
  
  
  // .
  // ├── config/              # contains the configuration files for the app
  // │   ├── default.json     # default configuration variables
  // │   ├── production.json  # override default configurations variables when NODE_ENV=production
  // │   └── ...
  // │
  // ├── node_modules/        # project dependencies using NPM or Yarn
  // │   └── ...
  // │
  // ├── public/              # contains static files to be served
  // │   └── ...
  // │
  // ├── src/                 # contains the Feathers server code
  // │   ├── hooks/           # contains our custom hooks
  // │   │   └── ...
  // │   ├── middleware/      # contains our Express middlewares
  // │   │   └── ...
  // │   ├── services/        # contains our services
  // │   │   └── ...
  // │   │
  // │   ├── index.js         # is used to load and start the application
  // │   ├── app.js           # configures our Feathers application
  // │   ├── app.hooks.js     # contains hooks which that run for all services
  // │   └── channels.js      # set up Feathers event channels
  // ├── tests/               # contains Mocha test files for the app, hooks and services
  // │   └── ...
  // ├── .editorconfig        # helps developers define and maintain consistent coding styles
  // ├── .eslintrc.json       # eslint configuration
  // └── package.json         # express server for production
  