Everything You Ever Wanted to Know About Javascript Filter Method

Everything You Ever Wanted to Know About Javascript Filter Method

Learn how to use the JavaScript Filter() method. How the fllter method of javascript works. When to use js filter method in the code. JS Array methods list

State Management with React Hooks and RxJS

State Management with React Hooks and RxJS

In this article, we’ll cover the basics of RxJS and how to integrate it with React applications using React Hooks for state management.

In this article, we’ll cover the basics of RxJS and how to integrate it with React applications using React Hooks for state management. We’ll do this by building a demo chat application. Our chat application will have three components that will communicate with each other through RxJS.

Our final app will look like this:

Let’s start by explaining RxJS

RxJS (Reactive Extensions Library for JavaScript) is a useful library for reactive programming. The RxJS documentation uses this definition:

RxJS is a library for reactive programming using Observables, to make it easier to compose asynchronous or callback-based code.

Reactive programming is an event-based paradigm that allows us to run asynchronous sequences of events as soon as data is pushed to a consumer.

To be able to use RxJS for state management in React, it is important to understand the following key terms:

Observable

An Observable is a data stream that houses data that can be passed through different threads. In our demo app, we’ll be using an Observable to supply data to our different components.

Observer

An Observer consumes the data supplied by an Observable. In our demo app, we’ll be using our setState Hook to consume data from our Observable.

Subscription

In order for our Observer to consume data from our Observable, we’ll have to subscribe it to the Observable. In our demo app, we’ll be using the subscribe() method to subscribe our setState Observer to our Observable.

Setting up our application

The best way to understand RxJS is to use it.

Let’s start by creating a new react application. If you don’t have create-react-app installed, on your terminal, run:

>npm i -g create-react-app

Next:

create-react-app rxjs_react_chat

This will generate a new react application using create-react-app.

To start our application, let’s navigate to our new app directory and run the command npm start:

cd rxjs_react_chat
npm start

In our new generated app directory, let’s navigate to /src/. Since we’ll be working with multiple components, let’s set up BrowserRouter for navigating through different routes.

Let’s run the following command:

npm install --save react-router-dom

Next, we’ll edit our /src/App.js file to look like this:

// /src/App.js
import  React  from  'react';
import { BrowserRouter, Route, Switch } from  'react-router-dom';
import  './index.css';

const  App  = () => (
  <BrowserRouter />
);

export  default  App;

In our src folder, let’s create a store directory, src/store. This is where we’ll house our store.

Next, let’s create a chat.js file for our chat operations, src/store/chat.js. In our chat.js file, we’ll import Subject from rxjs and create a new variable from the Subject class:

import { Subject } from 'rxjs';

const subject = new Subject();

Subjects and Subscriptions

An RxJS Subject can act as both an Observable and an Observer at the same time. In this way, values can be multicasted to many Observers from it so that when a Subject receives any data, that data can be forwarded to every Observer subscribed to it.

In our application, we’ll be subscribing our different React Hooks setState functions to our RxJS Subject so that when it receives any data, it forwards that data to every state associated with our setState function.

Let’s create a subscribe method for this purpose:

import { Subject } from 'rxjs'

const subject = new Subject();

const chatStore = {
  subscribe: setState => subject.subscribe(setState)
}

Next, we’ll create an object for our initial chat state:

import { Subject } from 'rxjs'

const subject = new Subject();

const initialState = {
  data: [],
  newDataCount: 0,
}; 

let state = initialState;

const chatStore = {
  subscribe: setState => subject.subscribe(setState)
}

We’ll use the data key to hold our array of message objects. These message objects will contain the values person (to specify who a message is from) and text (to store the message text).

Here’s what our object will look like:

{
  person: 'first-person',
  text: 'How are you?'
}

In our initialState object, the newDataCount will be used by our notification functionality to tell when new data has been pushed to our state.

Now that we have our state object, let’s create an init() method that will initialize our component’s state whenever it’s mounted:

...
const chatStore = {
  init: () => subject.next(state),
  subscribe: setState => subject.subscribe(setState)
}

The Subject.next() method is used to feed a new value to the Subject. When we call the next() method with a value as its parameter, that value is multicasted to all Observers subscribed to the Subject.

In our application, we’ll call both the subscribe() and init() methods whenever our component mounts in order to set our state to what we have in our chat store.

Adding data to the store

Next we’ll create a sendMessage() method. We’ll call this method whenever our users hit the send message button. Our sendMessage() method will receive a message argument, which we’ll append to our state.data array. Remember that our message argument is an object with keys person and text.

Let’s create our object with the following code block:

...
const chatStore = {
  init: () => subject.next(state),
  subscribe: setState => subject.subscribe(setState),
  sendMessage: message => {
    state = {
      ...state,
      data: [...state.data, message],
      newDataCount: state.newDataCount + 1
     };
     subject.next(state);
  }
};

In our new block, we appended our message object to our state.data array, then we incremented our newDataCount.

Now that we have our newDataCount incremented every time a new message is sent by a user, we’ll also add a functionality for resetting our new data count each time the messages are viewed so that when person 1 sends a new message and person 2 reads the message, the data count resets to 0.

To do this, in our init() method, we’ll assign the newDataCount key in our state the value of 0 each time a new component that subscribes to our Subject is mounted:

...
const chatStore = {
  init: () => {
    state = {...state, newDataCount: 0},
    subject.next(state)
  },
  subscribe: setState => subject.subscribe(setState),
  sendMessage: message => {
    state = {
      ...state,
      data: [...state.data, message],
      newDataCount: state.newDataCount + 1
    };
    subject.next(state);
  }
};

Removing data from the store

Next, we’ll add a method for clearing all messages. We’ll call it clearChat():

...
const chatStore = {
  init: () => {
    <b>state = {...state, newDataCount: 0},</b>
    subject.next(state)
  },
  subscribe: setState => subject.subscribe(setState),
  sendMessage: message => {
    state = {
      ...state,
      data: [...state.data, message],
      newDataCount: state.newDataCount + 1
    };
    subject.next(state);
  },
  clearChat: () => {
    state = initialState;
    subject.next(state);
  },
  initialState
};

We’ve also added our initial state to the chatStore object. We’ll use this to set our initial state value when defining our chatState with the useState() Hook.

Finally, let’s export the chatStore object. Our src/store/chat.js file should now look like this:

// src/store/chat.js

import { Subject } from 'rxjs';

const subject = new Subject();
const initialState = {
  status: '',
  data: [],
  newDataCount: 0,
  error: ''
};

let state = initialState;

const chatStore = {
  init: () => {
    state = {...state, newDataCount: 0}
    subject.next(state)
  },
  subscribe: setState => subject.subscribe(setState),
  sendMessage: message => {
    state = {
      ...state,
      data: [...state.data, message],
      newDataCount: state.newDataCount + 1
    };
    subject.next(state);
  },
  clearChat: () => {
    state = {...state, data: []};
    subject.next(state);
  },
  initialState
};

export default chatStore;
Using the store

Now that we’ve set up our chat store, in the following steps, we’ll be creating our components to utilize the store and its methods.

First, let’s modify our src/index.css file to look like this:

.container {
  font-family: Arial, Helvetica, sans-serif;
  padding: 1em;
}

.chat-box {
  background: #202020;
  margin: auto;
  padding: 2em;
  height: 35em;
  width: 95%;
  border-radius: 20px;
  overflow-y: scroll;
}

.first-person, .second-person {
  display: inline-block;
  color: #fff;
  height: 25px;
  min-width: 20%;
  max-width: 60%;
  padding: 20px;
  text-align: center;
  vertical-align: middle;
  border-radius: 30px;
}

.first-person {
  background: rgb(0, 173, 231);
}

.second-person {
  background: #06c406;
  float: right;
}

.clear{ 
  clear: both;
  display: block;  
  content: "";
  width: 100%;  
}

.switcher-div {
  padding-top: 1em;
  text-align: center;
}

#messageForm {
  text-align: center;
  margin-top: 1.5em;
}

#messageForm input {
  height: 2em;
  width: 23em;
  border-radius: 3em;
  padding: 1em;
}

#messageForm button {
  margin-left: 2em;
  height: 2.7em;
  width: 6.2em;
  border-radius: 25px;
  border: none;
  cursor: pointer;
}

.clear-button {
  background: #d40000;
  color: #fff;
  float: right;
  margin-right: 3em;
  text-align: center;
  height: 2.5em;
  width: 8em;
  cursor: pointer;
}

.switcher {
  background: #cecece;
  color: #141414;
  height: 2.5em;
  width: 6em;
  border-radius: 25px;
  border: 1 px solid black;
  margin-right: 1em;
  cursor: pointer;
}

.notify {
  position: absolute;
  background: #db0000;
  color: white;
  height: 1em;
  width: 1em;
  border-radius: 100%;
  padding: 0.15em;
  margin-left: 0.5em;
  margin-top: -0.5em;
}

In our src folder, let’s create a components directory, src/components. This is where we’ll house all our components. We’ll need three components for our application:

  • A component for the first person
  • A component for the second person
  • A component for switching between the two person components

In our src/components directory, let’s create a new file, FirstPerson.js, for our first person component. Our new component should look like this:

import  React, { useState } from  "react";

const FirstPerson = () => {
  const [chatState, setChatState] = useState({});
  return (
    <div className="container">
      <h2>Mycroft</h2>
      <div className="chat-box">
        {chatState.data.map(message => (
          <div>
            <p className={message.person}>{message.text}</p>
            <div className="clear"></div>
          </div>
        ))}
      </div>
      <form id="messageForm">
        <input
          type="text"
          id="messageInput"
          name="messageInput"
          placeholder="type here..."
          required
        />
        <button type="submit">Send</button> <br />
      </form>
    </div>
  );
}

export  default  FirstPerson;

Subscribing to our store and retrieving existing data

In the next block, we’ll import our chatStore and use its initialState property as our default chatState value.

Then, in our useLayoutEffect() Hook, we’ll subscribe our setChatState function to our chat store using the chatStore.subscribe() method and, finally, use the chatStore.init() method to initialize our component’s chatState:

import React, { useState, useLayoutEffect } from "react";
<b>import chatStore from '../store/chat';</b>

const FirstPerson = () => {
  const [chatState, setChatState] = useState(chatStore.initialState);

  useLayoutEffect(()=> {
    chatStore.subscribe(setChatState);
    chatStore.init();
  },[]);

  return (...)

We are making use of the useLayoutEffect() Hook to send data to our chatState before our component is rendered.

To preview the result of our code so far, let’s create an index.js file in our src/components folder and export our FirstPerson component from it:

// src/components/index.js
export {  default as FirstPerson } from './FirstPerson';

Next, we’ll import our FirstPerson component in our src/App.js file and add it to a route path:

// /src/App.js
import  React  from  'react';
import { BrowserRouter, Route, Switch } from  'react-router-dom';
import { FirstPerson } from './components';
import  './index.css';

const  App  = () => (
    <BrowserRouter>
      <>
        <Switch>
          <Route path="/" component={FirstPerson} exact />
          <Route path="/first-person" component={FirstPerson} exact />
        </Switch>
      </>
   </BrowserRouter>
);

export  default  App;

Now, when we run our app and navigate to the / or /first-person route, we should see:

Back to our /src/components/FirstPerson.js file. Let’s add an onFormSubmit() method. We’ll call this method whenever our user clicks the send button:

...

const FirstPerson = () => {
  const [chatState, setChatState] = useState(chatStore.initialState);

  useLayoutEffect(()=> {
    chatStore.subscribe(setChatState);
    chatStore.init();
  },[]);

  const onFormSubmit = e => {
    e.preventDefault();
    const messageObject = {
      person: 'first-person',
      text: e.target.elements.messageInput.value.trim(),
    };
    chatStore.sendMessage(messageObject);
    document.getElementById('messageForm').reset();
  };

  return (
    ...
      <form id="messageForm" onSubmit={onFormSubmit}>
        <input
          type="text"
          id="messageInput"
          name="messageInput"
          placeholder="type here..."
          required
        />
        <button type="submit">Send</button> <br />
      </form>
    </div>
  );
}

export default FirstPerson;

Our onFormSubmit() function creates a message object with the person and text keys, then uses our chatStore.sendMessage() method to add our new message to the chat store.

Next, we’ll add a button that we’ll use to call our chatStore.clearChat() method. We’ll use this to clear our chat store whenever the clear button is clicked.

Let’s add the following block of code right after the </form> closing tag:

<button className="clear-button" onClick={() => chatStore.clearChat()}>
  Clear Chat
</button>

Our src/components/FirstPerson.js file should now look like this:

import React, { useState, useLayoutEffect } from "react";
import chatStore from '../store/chat';

const FirstPerson = () => {
  const [chatState, setChatState] = useState(chatStore.initialState);

  useLayoutEffect(()=> {
    chatStore.subscribe(setChatState);
    chatStore.init();
  },[]);

  const onFormSubmit = e => {
    e.preventDefault();
    const messageObject = {
      person: 'first-person',
      text: e.target.elements.messageInput.value.trim(),
    };
    chatStore.sendMessage(messageObject);
    document.getElementById('messageForm').reset();
  };

  return (
    <div className="container">
      <h2>Mycroft</h2>
      <div className="chat-box">
        {chatState.data.map(message => (
          <div>
            <p className={message.person}>{message.text}</p>
            <div className="clear"></div>
          </div>
        ))}
      </div>
      <form id="messageForm" onSubmit={onFormSubmit}>
        <input
          type="text"
          id="messageInput"
          name="messageInput"
          placeholder="type here..."
          required
        />
        <button type="submit">Send</button> <br />
      </form>
      <button className="clear-button" onClick={() => chatStore.clearChat()}>
        Clear Chat
      </button>
    </div>
  );
}

export default FirstPerson;

When we preview our app on our browser, we should now be able to send a message to our store and clear all messages:

[IMAGE]

Sharing data among components

Now that we’ve seen how to retrieve data from our store and add data to it, let’s create our SecondPerson component to demonstrate how this data can be shared between different components.

The SecondPerson component has the same functionality as the FirstPerson component, so we’ll only change our person value in our messageObject to second-person and the name of our user from Mycroft to Cortana in the <h2> tag inside our container div.

To do this, let’s create a new file, src/components/SecondPerson.js, and paste the following code blocks:

import React, { useState, useLayoutEffect } from "react";
import chatStore from '../store/chat';

const SecondPerson = () => {
  const [chatState, setChatState] = useState(chatStore.initialState);

  useLayoutEffect(()=> {
    chatStore.subscribe(setChatState);
    chatStore.init();
  },[]);

  const onFormSubmit = e => {
    e.preventDefault();
    const messageObject = {
      person: 'second-person',
      text: e.target.elements.messageInput.value.trim(),
    };
    chatStore.sendMessage(messageObject);
    document.getElementById('messageForm').reset();
  };

  return (
    <div className="container">
      <h2 style={{float: 'right'}}>Cortana</h2>
      <div className="chat-box">
        {chatState.data.map(message => (
          <div>
            <p className={message.person}>{message.text}</p>
            <div className="clear"></div>
          </div>
        ))}
      </div>
      <form id="messageForm" onSubmit={onFormSubmit}>
        <input
          type="text"
          id="messageInput"
          name="messageInput"
          required
        />
        <button type="submit">Send</button> <br />
      </form>
      <button className="clear-button" onClick={() => chatStore.clearChat()}>
        Clear Chat
      </button>
    </div>
  );
}

Next, we’ll need to create our PersonSwitcher component to switch between our two components. In our src/components directory, let’s create a new file, PersonSwitcher.js, and paste the following code blocks:

// src/components/PersonSwitcher.js
import React, {useState, useEffect} from 'react';
import { Link } from 'react-router-dom';
import chatStore from '../store/chat';

const PersonSwitcher = () => {
  const [chatState, setChatState] = useState(chatStore.initialState);
  const location = window.location.href.split('/')[3];

  useEffect(() => {
    chatStore.subscribe(setChatState);
    chatStore.init();
  }, [])

  const messageNotification = chatState.newDataCount > 0
    && (<span className="notify">{chatState.newDataCount}</span>);

  return (
    <div className="switcher-div">
      <Link to="/first-person"><button className="switcher">
        Person1
        {location !== 'first-person' && location.length > 1 && messageNotification}
      </button></Link>
      <Link to="/second-person"><button className="switcher">
        Person2
        {location !== 'second-person' && messageNotification}        
      </button></Link>
    </div>
  );
}

export default PersonSwitcher;

Notice that we’ve also created a chatState for our component, which we’ve subscribed to our chatStore. We’ll need this to notify our component when a new message is added to our chat store. Note how we added a messageNotification variable that utilizes our newDataCount property from our chat store.

Now, we can export our two new components from our src/components/index.js folder:

export { default as FirstPerson } from './FirstPerson';
export { default as SecondPerson } from './SecondPerson';
export { default as PersonSwitcher } from './PersonSwitcher';

Finally, let’s import our new components in our src/App.js and add them to our BrowserRouter. Our App.js file should now look like this:

import React from 'react';
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import { FirstPerson, SecondPerson, PersonSwitcher } from './components';
import './App.css';

const App = () => (
  <Router>
    <>
      <PersonSwitcher />
      <Switch>
        <Route path="/" component={FirstPerson} exact />>
        <Route path="/first-person" component={FirstPerson} exact />>
        <Route path="/second-person" component={SecondPerson} exact />>
      </Switch>
    </>
  </Router>
);

export default App;

Now when we run our application, we’ll be able to switch between components, receive new message count when we send a message, and clear all messages using the clear button:

Conclusion

In this article, we’ve covered the basics of RxJS and have demonstrated how to use it for state management in React by building a component-based chat application. Here’s a link to the GitHub repo for our demo app.

Compared to other alternatives like Redux, I’ve found the use of RxJS and Hooks to be a really effective and straightforward way to manage state in React applications.

Angular vs. React: Rendering an Array

Angular vs. React: Rendering an Array

How Angular and React differ in rendering an Array. A comparison of methods rendering an Array. We often need to render an array in the UI. Angular does this by using *ngFor — an HTML construct. React does this by using map() — a JS method. That's about it for rendering arrays in Angular and React.

Scenarios Where You Need to Render an Array

No rocket science behind this — scenarios to render an array are commonplace. The array to render could be an array of heroes (see the mighty Heroes example). It could be an array of items to buy or chores to complete. Or a menu to render based on an array of options. Or maybe you are working for an insurance company and you have an array of plans to render. Perhaps you are creating an e-commerce website and you have items to render based on an array returned by a search operation. Arrays everywhere!

Angular’s Way: *ngFor

Angular uses a special HTML construct: *ngFor

Code


The array to render — TS file

Angular uses *ngfor to render an array — HTML file

Code explained

Line 6 sets up the *ngFor loop. It takes the first item of the plans array and renders lines 7 and 8 (in fact, any number of lines in between the tags where *ngFor is used — ul here) for it.

Step one is then repeated for each item in the array.

React’s Way: map()

React makes use of the JS map method for this purpose. What map() essentially does is to map (or transform) each element of the original array to the elements of a new array.

The essence of mapping operation

In other words, the map() transforms each item of the original array into elements of a new array.

Code


The array to render — JS file


Use of map to render an array in React

Code explained

Step 1. In effect, map() takes the first element of the plans array and puts it in the plan variable in line 48.

Step 2. It then creates a new array with the latter’s elements being:

  • {{plan.name}} — ${{plan.premiumInDollars}}
  • Validity in years: {{plan.validityInYears}}

    Thereafter, map() repeats steps 1. and 2. for each element of the original array.

    map() in action

    Edit: We need keys too while rendering an Array in React. See my piece on React keys here.

    Full Examples Angular

    https://stackblitz.com/edit/angular-ngfor-sample-example?embed=1&file=src/app/app.component.ts

    React

    https://stackblitz.com/edit/react-map-example?embed=1&file=index.js

    Summary

    We often need to render an array in the UI.

    Angular does this by using *ngFor — an HTML construct.

    React does this by using map() — a JS method.

    That’s about it for rendering arrays in Angular and React.

    Happy coding!

    Originally published by Aanchal Kapoor at https://medium.com

    Microfrontends — Connecting JavaScript frameworks together (React, Angular, Vue etc)

    Microfrontends — Connecting JavaScript frameworks together (React, Angular, Vue etc)

    React, Angular, Vue, Ember, Backbone, Stencil, Preact…. in fact there’s probably another one being released right now. Microfrontends — bringing JavaScript frameworks together (React, Angular, Vue etc)

    Like most things in life, a variety of choices informs a toxic culture of mine is better than yours and you’re wrong and I’m right.

    Since technology advancements have got us in this mess, is there any chance it could get us out of it as well?

    Enter Microfrontends…

    Introduction to Microfrontends

    Modern UI development regardless of your framework has became all about component composition: You adapt to a framework’s way of doing things by following their patterns and conventions to create components usually underpinned by some sort of data model usually in the form of a service or state object.

    For example: Angular has a strong opinion on how everything should be architected in the frontend. React although it only deals with components has a huge ecosystem backing it driven by a community of React-centric developers.

    **Microfrontends **have gathered huge momentum recently as away of allowing multiple teams to work on a single UI using multiple frameworks, but could it really change the landscape of UI development?

    In this article, I am going to spend some time looking at the SDLC (software development lifecycle) and the advantages of adopting such an architecture.

    Where’s the problem?

    The current trend in UI development, is to build a feature-rich and powerful browser application (single page application) using a chosen framework.

    Development results in building lots of little components which are then bundled together in some sort of build process using something like webpack or rollup.

    Over time the UI layer often developed by separate or multiple teams, grows and gets more difficult to maintain creating a huge monolithic frontend.

    Monolithic frontend SDLC

    Monolithic frontends deployment architecture

    Reversing the microservice anti-pattern:

    Microfrontends looks at removing that monolithic build step, and results in completely decoupled services that can be independently built and deployed:

    Microfrontend SDLC

    Microfrontend deployment architecture

    Now our UI architecture has all the qualities of traditional microservices:

    • Highly maintainable and testable
    • Loosely coupled
    • Independently deployable
    • Organised around business capabilities
    How could this bring the big frameworks together?

    Since we have decoupled our UI components into many microfrontends, we no longer have to dictate which framework each component uses.

    The below illustration shows how we could potentially have different application teams using different technologies to create their independently built and released microfrontend:

    SDLC using multiple frameworks

    There are **several ways **to solve this using technologies but let me illustrate one example:

    1. **Develop: **Three teams using a different JavaScript framework for each microfrontend
    2. Build: Wrapping their microfrontend components as web components*** ***and building their project as a JavaScript file
    3. Release: A single JavaScript file is released inside a docker container served using Ngnix

    Once we have released our microfrontends, we should compose them together in a single UI layer. The communication between the microfrontends should be handled by the composition layer which should have a well defined contract.

    Deployment architecture using multiple frameworks

    From a user perspective they access a single application, but the developer’s ability to solve a problem is no longer limited by what single framework the application uses.

    Thanks for reading

    If you liked this post, please do share/like it with all of your programming buddies!

    Follow us on Facebook | Twitter

    Further reading about JavaScript

    The Complete JavaScript Course 2019: Build Real Projects!

    Vue JS 2 - The Complete Guide (incl. Vue Router & Vuex)

    JavaScript Bootcamp - Build Real World Applications

    The Web Developer Bootcamp

    New ES2019 Features Every JavaScript Developer Should Know

    Best JavaScript Frameworks, Libraries and Tools to Use in 2019

    Top 50 Interview Questions for JavaScript Developer

    Vue.js Tutorial: Zero to Sixty

    React vs Angular vs Vue.js by Example

    Build a Basic CRUD App with Vue.js and Node