React Native Seed

This project uses:

• React for rendering views
• Redux for state managment
• Redux Observable / Rxjs for side effecst and data flows

Standards

• Git Flow, please read git-workflow.
• Code reviews template. This is a standard format:

If any field below is not needed, keep the title and use N/A as message body.

## Background
_(Explain what was the problem, what decisions you took to solve them.)_
## Changes done
_(Enumerate changes done, that are not obvious from the contents of the code. Explain only general approaches to the changes. Explain design decisions if any.)_
## Pending to be done
_(Enumerate known pending tasks and why they weren't addressed here.)_
## Notes
_(Optional. Any additional notes that will help reviewers understand the PR.)_

Commands

• installation: yarn install
• develop: yarn start:dev starts the app on development mode
• android yarn android install app on device
• test: yarn test unit tests
• test: yarn test -u unit tests with snapshots update. Make sure you really need to update the snapshots by checking the error messages thoroughly
• build-config: yarn build-config<environment> build app.json and config.json based on the environment(development, qa, stage, production, test)

Scaffolding

• App.tsx (file) app root, this only imports our own app root and should never be changed
• app.json (file) expo config file containing that partially changes dinamically depending on the env
• src (folder) source code
• • assets (folder) media assets
• • config (folder) environment config files
• • • <env>.config.json (file) env vars to be written on config.json depending on the env
• • constants (folder) app constants
• • modules (folder) main app modules
• • • models (folder) entity models, typeguards, interfaces, enums, and other ts related files
• • • services (folder) services that will be injected as dependencies to be used on epics
• • • state-mgmt (folder) state management files grouped by entity and store creation
• • • views (folder) react components grouped by page and shared folder including cross app components
• • test (folder) testing helpers and mocks
• • types (folder) general types that doesn't feet any model. This is rarely used
• • utils (folder) utilities

Code Examples

Models

• Definition files for interfaces groped by namespace
• Static typing advantages

/** namespace to group interfaces */
export namespace UserModel {
  export enum Status {
    ONLINE = 'online',
    OFFLINE = 'offline'
  }

  /** this is how all user objects should look */
  export interface IUser {
    id?: string; // optional id field, because it's not there on entity creation
    email: string;
    name: string;
    status: Status;
  }
}

Services

• Classes to help on epics (rxjs side effects) to achieve several things as http requests, access to the logger, etc.
• They can be static or not depending on the needs, they are injected (instantiated) on the store file state-mgmt/store.ts (code example is shown later on this file)

/** Logger */
import { ENV } from '../../constants';
import { EventTracker } from './EventTracker';

export abstract class Logger {
  private static shouldLog = !ENV.IS_TEST;
  private static printer = console;

  public static log = (...args) => Logger.logMethod('log', ...args);
  public static info = (...args) => Logger.logMethod('info', ...args);
  public static warn = (...args) => Logger.logMethod('warn', ...args);
  public static error = (...args) => Logger.logMethod('error', ...args);
  public static table = (...args) => Logger.logMethod('table', ...args);

  private static logMethod = (level, ...args) => {
    EventTracker[EventTracker[level] ? level : 'debug'](...args);
    if (!Logger.shouldLog) return;
    Logger.printer[level](...args);
  }

}

State-mgmt

• It groups all redux files in the app by entity
• It uses redux-observable middleware to emit actions into rxjs observables called epics which emites actions in return
• The side effect flow looks like this:
• • action GET_USER_START was dispatched into the redux store
• • an epic received that action as an observable emition > then called the server > then emited a new action GET_USER_SUCCESS which will be dispatched into the redux store
• • a reducer with a switch case for GET_USER_SUCCESS adds the user to the user's state

actions

• Actions are payloads of information that send data from the application to the store

/** Action types constants */
export enum ActionType {
  GET_START = '[user] get start',
  GET_SUCCESS = '[user] get success'
}
/** action creators */
export const actions = {
  getStart: (userId: string) => ({ type: ActionType.GET_START, payload: { userId } }),
  getSuccess: (user: UserModel.IUser) => ({ type: ActionType.GET_SUCCESS, payload: { user } })
};

epic

• Function that returns an rxjs observable that expects to receive an action and emits n actions
• • action$ is an observable that emits redux actions
• • state$ is an observable containing the current redux state. It is usually accesed like this: state$.value.auth.currentUserId

export const userGetEpicGetUserList: Epic<IAction, IAction, IRootState, IEpicDependencies> = (action$, state$, deps) => // returns an observable
  action$.pipe( // pipes the action observable to change the flow
    ofType(ActionType.SET_LIST_START), // filter to get only ActionType.SET_LIST_START emitions
    mergeMap(action => of(null).pipe( // mergeMap to a new observable pipe in case it throws an error and completes, the next SET_LIST_START will still be listened to
      mergeMap(({ payload }) => deps.apiService.getUserList(payload.idList)), // merges with the apiService observable
      map(res => actions.setListSuccess(res.docs)), // maps the server's response into an action object { type: 'action type string' payload: { user: <user data> } }
      catchError(error => of(coreState.actions.epicError(error))) // catches error, completes this pipe and emits an action object { type: 'error type', payload: <error payload> } as the final value
    ))
  );

reducer

• straightforward redux reducer
• we use maps instead of lists so we avoid looping, repeated values, select easly, check for thruthy values, compose with other states, etc.

import { IState, initialState } from './state';
import { ActionType } from './actions';

export const reducer = (state: IState = initialState, { type, payload }: { type: ActionType, payload: any }): IState => { // this return type helps writing reducers using standard ts advantages
  switch (type) {
    case ActionType.SET_LIST_SUCCESS:
      return { ...state, userMap: payload.userList.reduce((total, item) => ({ ...total, [item._id]: item }), state.userMap) };
    case ActionType.SET_SUCCESS:
      return { ...state, userMap: { ...state.userMap, [payload.user._id]: payload.user } };
    default:
      return state;
  }
};

store

• Standard redux store with the added responsibility of creating the provider for the dependency injection on epics

import { combineReducers, createStore, applyMiddleware, Store } from 'redux';
import { createEpicMiddleware, combineEpics } from 'redux-observable';
import { composeWithDevTools } from 'redux-devtools-extension';

import { ApiService } from '../services/ApiService';
import { Logger } from '../services/Logger';
import { IRootState, IEpicDependencies, authState, userState, coreState } from './rootState';

/** combining epics (observable getters) to use as middeware */
const rootEpic = combineEpics<any>(...authState.epics, ...coreState.epics, ...userState.epics);

/** provides for DI */
const epicMiddleware = createEpicMiddleware({
  dependencies: {
    apiService: new ApiService(),
    logger: Logger
  } as IEpicDependencies
});

const withDevtools = composeWithDevTools({ maxAge: 20, shouldCatchErrors: true });

const store: Store = createStore<IRootState, any, any, any>(
  combineReducers({ auth: authState.reducer, user: userState.reducer } as any), withDevtools(applyMiddleware(epicMiddleware))
);

export { store };

epicMiddleware.run(rootEpic); // starts epic middleware so it subscribes to actions being dispatched

views

• Composed of components and containers to render views

containers

• containers are the connection between redux (state and action dispatchers)
• they handle the selection and composition of data needed to render
• the DO NOT contain tsx/jsx or other react code

import { connect } from 'react-redux';

import { MessageModel } from '../../models';
import { IRootState, messageState } from '../../state-mgmt/rootState';
import Communication from './Communication';

export const mapStateToProps = (state: IRootState) => ({
  messageMap: state.message.messageMap, // straightforward selection
  currentUser: state.user.userMap[state.auth.currentUserId] // composition using user and auth states
});

export const mapDispatchToProps = dispatch => ({
  sendMessage: (message: MessageModel.IMessage) => dispatch(messageState.actions.setStart(message))
});

export default connect(mapStateToProps, mapDispatchToProps)(Communication);

components

• React components, mostly presentational with little to no business logic
• Components try to be as dumb as possible, delegating all complex tasks to:
• • epics through containers to fetch, create data or other flows
• • helpers/utils for agnostic logic like parsing, formatting, calculating, etc
• • child components for reusable renders, branching or other render related tasks

import * as React from 'react';

import styles from './styles';

export interface ILoginProps {
  login: (username: string, password: string) => void;
}

export interface ILoginState {
  username: string;
  password: string;
}

export default class Login extends React.PureComponent<ILoginProps, ILoginState> {
  public state: ILoginState = { username: '', password: '' };

  public login = () => {
    const { login } = this.props;
    const { username, password } = this.state;
    login(username, password);
  }

  public setUsername = (event: React.ChangeEvent<HTMLInputElement>) => {
    this.setState({ username: event.target.value });
  }
  public setPassword = (event: React.ChangeEvent<HTMLInputElement>) => {
    this.setState({ password: event.target.value });
  }

  public render() {
    const { username, password } = this.state;
    return (
      <div style={styles.loginContainer}>
        <form style={styles.loginForm}>
          <input style={styles.loginInput} onChange={this.setUsername} value={username} placeholder="username" type="text" />
          <input style={styles.loginInput} onChange={this.setPassword} value={password} placeholder="password" type="password" />
          <button style={styles.loginButton} onClick={this.login} type="button">Login</button>
        </form>
      </div>
    );
  }
}

test

• tests aim to achieve 100% coverage and have examples for each test scenario that might occur

Service

import { Logger } from './Logger';

describe('Logger', () => {
  beforeEach(() => {
    (Logger as any).printer = { log: jest.fn(), info: jest.fn(), warn: jest.fn(), error: jest.fn(), table: jest.fn() };
  });

  it('should log with all logging methods', () => {
    const data = 'well hello..';
    Logger.log(data);
    expect((Logger as any).printer.log).toHaveBeenCalledWith(data);
    Logger.info(data);
    expect((Logger as any).printer.info).toHaveBeenCalledWith(data);
    Logger.warn(data);
    expect((Logger as any).printer.warn).toHaveBeenCalledWith(data);
    Logger.error(data);
    expect((Logger as any).printer.warn).toHaveBeenCalledWith(data);
    Logger.table(data);
    expect((Logger as any).printer.table).toHaveBeenCalledWith(data);
  });
});

Epic

describe('auth epics', () => {
  let deps: IEpicDependencies;
  let error;
  beforeEach(() => {
    error = new Error('scary error');
    deps = getDeps(); // fresh dependency mocks from the test helpers
  });

  describe('authGetEpicAuthStart', () => {
    const email = 'email';
    const password = 'password';

    it('should get epic for auth start', done => {
      const emitedActions = [];
      const loginResponse = getLoginResponse();
      const action$ = ActionsObservable.of(actions.start(email, password));
      authGetEpicAuthStart(action$, {/** if we need a mock state, this is the place to put it */} as any, deps).subscribe(output => {
        emitedActions.push(output); // we save each emision here
        if (output.type === ActionType.SET_LOADING && output.payload.isLoading === false) { // we chouse on which emision to stop and test
          expect(deps.apiService.login).toBeCalledWith({ email, password });
          expect(deps.asyncStorageService.setItem).toBeCalledWith(ENV.STORAGE_KEY.AUTH, { userId: loginResponse._id });
          expect(emitedActions[0]).toEqual(actions.setLoading(true));
          expect(emitedActions[1]).toEqual(actions.success(loginResponse._id, loginResponse.notificationChannel, loginResponse.defaultChannelId));
          expect(emitedActions[2]).toEqual(coreState.actions.bootstrap(loginResponse.access_token));
          expect(emitedActions[3]).toEqual(actions.setLoading(false));
          done();
        }
      });
    });

    /** we also test the catchError branch */
    it('should catch errors and dispatch them to the auth error handler', done => {
      const emitedActions = [];
      deps.apiService.login = () => { throw error; };
      authGetEpicAuthStart(ActionsObservable.of(actions.start(email, password)), {} as any, deps).subscribe(output => {
        emitedActions.push(output);
        if (output.type === ActionType.SET_LOADING && output.payload.isLoading === false) {
          expect(emitedActions[0]).toEqual(actions.setLoading(true));
          expect(emitedActions[1]).toEqual(actions.fail());
          expect(emitedActions[2]).toEqual(actions.setLoading(false));
          done();
        }
      });
    });
  });
});

Reducer

import { reducer } from './reducer';
import { initialState } from './state';
import { actions } from './actions';
import { getUser_1 } from '../../../test/entities';

describe('user reducer', () => {
  it('should return state without mutations when no switch case matches', () => {
    expect(reducer(initialState, { type: null, payload: null })).toBe(initialState);
  });

  it('should return a new state ActionType.SET_LIST_SUCCESS', () => {
    const user = getUser_1();
    expect(reducer(undefined, actions.setListSuccess([user]))).toEqual({ ...initialState, userMap: { [user._id]: user } });
  });

  it('should return a new state ActionType.SET_SUCCESS', () => {
    const user = getUser_1();
    expect(reducer(undefined, actions.setSuccess(user))).toEqual({ ...initialState, userMap: { [user._id]: user } });
  });
});

Container:

/** START the container looks like this */
import { connect } from 'react-redux';

import { IRootState, channelState } from '../../state-mgmt/rootState';
import About from './About';

export const mapStateToProps = (state: IRootState) => ({
  defaultChannelId: state.auth.defaultChannelId
});

export const mapDispatchToProps = dispatch => ({
  openChannel: (channelId: string) => dispatch(channelState.actions.openChannel(channelId))
});

export default connect(mapStateToProps, mapDispatchToProps)(About);
/** END the container looks like this */

import { mapStateToProps, mapDispatchToProps } from './AboutContainer';
import { IRootState, channelState } from '../../state-mgmt/rootState';
import { getState } from '../../../test/entities'; // mock state generated with mock entities

describe('AboutContainer', () => {
  let state: IRootState;
  beforeEach(() => {
    state = getState();
  });

  /** testing the state is maping the correct data to prop */
  it('should mapStateToProps, ', () => {
    expect(mapStateToProps(state)).toEqual({
      defaultChannelId: state.auth.defaultChannelId
    });
  });

  /** testing that props that contain dispach functions are there */
  it('should mapDispatchToProps', () => {
    const dispatch = jest.fn();
    const props = mapDispatchToProps(dispatch);
    expect(props).toEqual({
      openChannel: expect.any(Function)
    });
  });

  /** testing that the correct actions are being dispatched */
  it('should openChannel', () => {
    const dispatch = jest.fn();
    const props = mapDispatchToProps(dispatch);
    props.openChannel(state.auth.defaultChannelId);
    expect(dispatch).toBeCalledWith(channelState.actions.openChannel(state.auth.defaultChannelId));
  });
});

Component

• for most of component testing, we are using snapshots
• a snapshot is created for each version of the render so we cover all branches

import * as React from 'react';
import { shallow } from 'enzyme';
import { create } from 'react-test-renderer';

import Login from './Login';

describe('Login Component', () => {
  let Component;
  let defaultProps;

  beforeEach(() => {
    defaultProps = {
      login: jest.fn()
    };
    Component = shallow(<Login {...defaultProps} />);
  });

  describe('render', () => {
    /** if we had more branches... like a render with and without error messages, we would have another snapshot */
    it('should render with default props', () => {
      expect(create(Component).toJSON()).toMatchSnapshot();
    });
  });

  describe('methods', () => {
    it('should set username and password and login', () => {
      const username = 'username';
      const password = 'password';
      Component.find('input[type="text"]').simulate('change', { target: { value: username } });
      Component.find('input[type="password"]').simulate('change', { target: { value: password } });
      expect(Component.instance().state).toEqual({ username, password });
      Component.find('button').simulate('click');
      expect(defaultProps.login).toBeCalledWith(username, password);
    });
  });
});

This section contains a guide of what we use to generate the react native application

• This project includes the following features:

• React Native mobile apps using TypeScript and React

• • expo build cross-platform native apps
• • redux predictable state container for JavaScript apps
• • rxjs reactive programming using Observables, to make it easier to compose asynchronous or callback-based code
• • rollbar real-time error alerting & debugging
• • jest unit testing