Introduction to React

React is a very popular JavaScript library for building user interfaces

Pre-requisites

• HTML
• JavaScript

Why React?

React was introduced by Facebook in 2013. Due to its readable syntax & code re-usability, it has become one of the most popular & most used libraries for front-end development.
React has a very strong community on the internet world so most issues during development are solved quickly.
React is easy to learn as its JSX (JavaScript XML) syntax is very close to HTML and enhances the confidence of a novice developer.

Basic Concepts of React

We will discuss some basic fundamental concepts of React:

1. Components

Components are building blocks of a React app. A component has one or more than one element of HTML to re-use it wherever needed. With the use of components, we get rid of writing redundant code. There are two types of components:

• Class Components
• Functional Components

2. JSX

JSX is a way to write React code. As from its name we can understand it's a mixture of JavaScript and XML as a result of a syntax which is easy to understand
For example:

const element = <h1>Welcome to React World!</h1>;

3. Props

Props are arguments we can pass into React components. Basically props are used for connecting different components by passing some value as an attribute to a React component.
One component can pass value in the other

4. State

State is the heart of a React app. Basically, state is used to store data which is required in our React component. Using state, changes in data can be seen in real-time without refreshing webpage

Enough Talk, Let's Code

We will build a simple React app which shows a list of quotes with their authors. We can add a quote and see a live update in the quotes table.
Let's start by creating a simple React app by running this command:

yarn create react-app my-app

This creates a React app named my-app with a built-in folder structure. In project folder, run :

yarn start

This starts your app at http://localhost:3000/
A simple React app has been created but we will customize it!
Open this folder in your favourite code editor.
Remove everything from return statement of App.js and refactor code as:

import React, { useState } from "react";
import AddQuoteForm from "./components/AddQuoteForm";
import { data } from "./components/Data";
import QoutesTable from "./components/QoutesTable";
import "./App.css";
function App() {
  const [quotesList, setQuotesList] = useState(data);
  const addQuote = (quote, author) => {
    const quoteObject = { quote: quote, author: author };
    setQuotesList([...quotesList, quoteObject]);
  };
  return (
    <div>
      <QoutesTable quotesList={quotesList} />
      <AddQuoteForm addQuote={addQuote} />
    </div>
  );
}
export default App;

App.js returns a div containing two React components. Let's create these components.
Inside the src directory, create a folder components. Inside it, create a file named QuotesTable.js and add following code:

import React from "react";
function QoutesTable(props) {
  return (
    <table>
      <thead>
        <tr>
          <th>Quote</th>
          <th>Author</th>
        </tr>
      </thead>
      <tbody>
        {props.quotesList.map((quote) => (
          <tr>
            <td>{quote.quote}</td>
            <td>{quote.author}</td>
          </tr>
        ))}
      </tbody>
    </table>
  );
}
export default QoutesTable;

This component will render quotes table. map function iterates each element of quotesList array and returns a tr containing quote and its author.
Residing in components directory, create a file named Data.js and add some dummy data in it:

export const data = [
  {
    quote:
      "Start writing, no matter what. The water does not flow until the faucet is turned on.",
    author: "Louis L'Amour",
  },
  {
    quote:
      "Get it down. Take chances. It may be bad, but it's the only way you can do anything really good.",
    author: "William Faulkner",
  },
  {
    quote: "The first draft is just you telling yourself the story.",
    author: "Terry Pratchett",
  },
];

Now create a component named AddQuote.js and write following code:

import React, { useState } from "react";
function AddQuoteForm(props) {
  const [quote, setQuote] = useState("");
  const [author, setAuthor] = useState("");
  const handleClick = () => {
    props.addQuote(quote, author);
    setQuote("");
    setAuthor("");
  };
  return (
    <div className="add-quote-form">
      <div>
        <label>Quote</label>
        <input
          type="text"
          value={quote}
          onChange={(e) => setQuote(e.target.value)}
        />
      </div>
      <div>
        <label>Author</label>
        <input
          type="text"
          value={author}
          onChange={(e) => setAuthor(e.target.value)}
        />
      </div>
      <button onClick={handleClick}>ADD</button>
    </div>
  );
}
export default AddQuoteForm;

This component will create a form to take quote and author as inputs and on button click, quote will be appended to the quotes table. This update will be real-time.
This is the beauty of React!
Remove everything from App.css and add the following code for better representation.

table,
th,
td {
  border: 1px solid black;
  border-collapse: collapse;
}
th,
td {
  padding: 1rem;
}
table {
  border-spacing: 5px;
  width: 50%;
  margin-left: 25%;
  margin-top: 1rem;
}
.add-quote-form {
  width: 50%;
  margin-left: 25%;
  margin-top: 1.5rem;
}
.add-quote-form input {
  width: 100%;
  margin-top: 0.25rem;
  margin-bottom: 0.25rem;
  height: 1.5rem;
}

Hurraaay! You just wrote your first React program.