Simplifying Web Applications with Progressive Web App Technology

Introduction

The current web technology landscape is dominated by JavaScript (JS) libraries, enabling developers to create highly engaging and intuitive web applications. Among these, React stands out as a powerful library that identifies application state changes and provides tailored views accordingly. Two tech giants, Facebook and Instagram, leverage React to create Progressive Web Applications (PWA) – a hybrid of websites and applications that aims to deliver an optimal user experience.

Aspiring to create your own PWA? There are numerous JS libraries at your disposal, including Angular.js, Vue.js, and React.js. However, for this discussion, we’ll center our focus on React, one of the most actively used software libraries today. Enhance your development process by incorporating React Developer Tools, which are browser-specific and can be downloaded from sources like the Chrome Store.

Diving Deeper into React

React fundamentally serves as a JavaScript library, specializing in constructing user interfaces. It enables the creation of reusable components which exhibit data transformations over time. If you’re a novice to React, you’ll find a wealth of knowledge and development assistance on Reactjs.org.

One of the key aspects of React is its interaction with the Document Object Model (DOM). The DOM sets the structural framework of HTML elements, and its Application Programming Interface (API) outlines how these elements can be updated and manipulated. React enhances the efficiency of updating the DOM through a technique known as DOM Diffing.

During DOM Diffing, the browser compares the rendered content with the impending UI changes (for instance, a form submission). React identifies the differences and updates only the minimal changes required, leading to speed optimization. DOM Diffing compares the JavaScript objects, ensuring faster changes than when manipulating objects on the DOM.

To put it simply, React acts as an intermediary between the DOM and the JavaScript logic layer. So, whenever we interact with the DOM using JavaScript (such as using getElementByID or changing classes), we’re actually engaging with the React.js virtual DOM. This mechanism interprets our requests and updates the physical DOM only when necessary, thus minimizing slow DOM updates.

Local React Project Setup

To work with React effectively, you need a well-oiled build workflow. This will ensure your code is optimized and make use of the latest features, aiding faster development, easing usage, and minimizing errors.

The tools needed include:

A Dependency Management Tool: This can be either NPM (Node Packet Manager) or Yarn. For our case, we’ll use NPM due to its familiarity.
A Bundler: Webpack will be our choice here. It allows us to write module code and distribute it across the application.
A Compiler: We’ll use Babel for this purpose. Babel translates our next-gen JavaScript into code that’s compatible with a wider range of browsers.
A Local Development Server: It helps test our code and run apps locally, offering performance benefits and enabling hot-refreshing the server.

The create-react-app repository, created by Facebook, is an excellent way to integrate all these tools. After installing it via NPM, you can run ‘create-react-app app-name’ from the development folder to start a new project.

Working with JSX and Components

JavaScript as XML (JSX) is a syntax hybrid that merges HTML and JavaScript, allowing faster component writing. It lets you insert HTML (mostly) within your JS file, with Babel transpiling the code into functional JS. HTML element tags can be used, and classes can be applied to elements by replacing the ‘class’ keyword (already reserved in JS) with ‘className’.

In React, all elements are components – reusable website sections. The simplest component is a function that returns JSX. When designing components, it’s crucial to follow best practices such as groupingrelated components in a folder, capitalizing the first letter of a component name at the folder and file level, using descriptive names to indicate the purpose of the component, and ensuring your function inside your component shares the same name as the component itself.

React Components and Props

Components receive properties, or ‘props,’ which are pulled into the component and interpolated. For instance, consider a Person component <Person>. If the return from person is <p>I’m {name} and I am {age} years old!</p>, you can pass data from the component to the function by setting an attribute <Person name=”James” age=”34″/>. To access the attribute from the props object (typically named ‘props’), use a statement like <p>I’m {props.name} and I am {props.age} years old!</p> to access the attributes as properties of an object for the return.

Also, you can write HTML between the opening and closing component tags. Something like <Person>I’m Super Cool</Person> can be accessed by using the ‘children’ property from the props argument. This means {props.children} will return anything written between the component tags.

States and React Components

While ‘props’ are passed in from outside the component, ‘state’ is managed within the component. ‘State’ is a JavaScript object and is particularly useful for components created by extending the base Component. However, the use of state should be done with care and, whenever possible, components should be created using arrow functions.

Debugging Errors

There are several types of errors that may occur during React development:

Error Messages: Always check the console for errors. Most of the time, you’ll get a line number which will help you pinpoint where the error occurred in your code.
Undefined Property Errors: This error occurs when you try to access a property on an object that is undefined.
Logic Errors: These do not throw error messages, but break functionality. It’s advisable to use the sources panel on the web developer toolbar to troubleshoot these issues.
Error Boundaries: They come into play when you’re working with APIs or receiving data from third-party servers. In cases where the data source might fail, you need to handle the error gracefully using Error Boundaries.

Understanding Components

Components in React should be as specific as possible and, if viable, should only control one thing. The root App component should majorly handle the management of the state, with minimal UI elements. Organize your code by using folders that better explain what is happening in your App. For example, a ‘Person’ folder can handle the logic of a person card, while a ‘Persons’ folder can handle the list of Persons.

Functional (Stateful) Components vs Stateless Components

Stateful components are containers that extend the base Component class, have access to the state property and lifecycle hooks, and allow us to access State and Props via the ‘this’ keyword. However, you should only use stateful components if you need to access state or lifecycle hooks.

In contrast, stateless components are functions that receive props, with no access to the state property or lifecycle hooks. They access state or props methods with the ‘props’ keyword. Wherever possible, it’s recommended to use stateless components in your project.

React Component Lifecycle

When a React component is being created and inserted into the DOM, it goes through several lifecycle methods:

constructor(): This method is called before the component is mounted. When implementing the constructor for a React.Component subclass, you should call super(props) before any other statement. Here, you can also initialize the state, but avoid any side effects (like API calls).
componentWillMount(): This method is now considered unsafe and is discouraged for use. It gets called right before the component gets mounted to the DOM.
render(): This is the only required method in a class component. It examines this.props and this.state and returns one of the following types: React elements, arrays and fragments, portals, string and numbers, booleans or null.
componentDidMount(): This method is invoked immediately after a component is mounted. If you need to load data from a remote endpoint, this is a good place to instantiate the network request.

Then there are lifecycle methods that get called when a component is being re-rendered as a result of changes to either its props or state.

componentWillReceiveProps(nextProps): This method is now considered unsafe and is discouraged for use. It is invoked before a mounted component receives new props.
shouldComponentUpdate(nextProps, nextState): This method is invoked before rendering when new props or state are being received. It returns a boolean value that indicates whether React should continue with the rendering or not.
componentWillUpdate(nextProps, nextState): This method is now considered unsafe and is discouraged for use. It is invoked just before rendering when new props or state are being received.
componentDidUpdate(prevProps, prevState): This method is invoked immediately after updating occurs. This method is not called for the initial render.

There are some lifecycle methods that React calls when a component is being unmounted.

componentWillUnmount(): This method is invoked immediately before a component is unmounted and destroyed.

Lastly, componentDidCatch(error, info) which is used for catching errors during rendering, in lifecycle methods, and in constructors of the whole tree below them.

To convert a functional component to a stateful component, you will need to create a class that extends React.Component, define a render method within it that returns the JSX code, and export this class as a default export.

React Update Lifecycle

There are two reasons why a component might be re-rendered: the state of the component has changed or the props provided to the component have changed. When an update is triggered:

componentWillReceiveProps(nextProps): This method is called before a mounted component receives new props. Remember, this method is considered unsafe and discouraged for use.
shouldComponentUpdate(nextProps, nextState): This method is called whenever a component is about to update due to changes in state or props.
componentWillUpdate(nextProps, nextState): This method is called just before the component re-renders due to changes in either state or props. It’s worth mentioning that this method is considered unsafe and discouraged for use.
render(): The component’s render method is called to generate the new representation of the component.
componentDidUpdate(prevProps, prevState): This method is called after the component re-renders. It is a good place to perform operations that need to happen after the component updates, such as fetching new data in response to prop changes.

PureComponents

React.PureComponent is similar to React.Component. The difference between them is that React.Component doesn’t implement shouldComponentUpdate(), but React.PureComponent implements it with a shallow prop and state comparison. If your component’srender() function renders the same result given the same props and state, you can use React.PureComponent for a performance boost in some cases.

React’s Rendering and Updating Process

React’s render method is what takes your components and returns the HTML to render on the page. However, it doesn’t immediately modify the DOM. Instead, it first creates a “virtual DOM” and diffs this with the current DOM to determine what changes need to be made. This approach minimizes interaction with the actual DOM (which is slow) and improves performance.

Higher Order Components

A higher-order component (HOC) is an advanced technique in React for reusing component logic. HOCs are not part of the React API. They are a pattern that emerges from React’s compositional nature. Essentially, a HOC is a function that takes a component and returns a new component with additional properties or behaviors.

Using setState Correctly

setState() is the primary method you use to update the state, leading to an update of the UI. It’s important to remember that setState() is asynchronous. This means if you attempt to access this.state immediately after calling setState(), you might not get the updated state. If you need to perform an action immediately after setting state, you can use a callback function with setState().

Props Validation

PropTypes were originally included in the React core but were later separated into a different package. PropTypes allow you to run typechecking on the props for a component to make sure that they are of an expected type. This is particularly useful during development for catching errors.

Using Refs

Refs provide a way to access DOM nodes or React elements created in the render method. They can be useful in certain situations, but should be used sparingly as they can lead to less clear code.

Planning React Apps

When planning a React app, you should think about your component structure, the state your app will need to maintain, and where that state lives. Here’s a general process:

Component Tree / Component Structure: Start by mapping out the components you’ll need and how they’ll be organized in the tree.
Application State: Identify the minimal representation of the state your application needs and where it should live.
Components vs. Containers: Decide which components should be stateless functional components and which should be stateful containers. Stateful components usually contain state that is relevant to many parts of your app, while stateless components are primarily concerned with rendering UI and triggering any necessary actions.

Reaching Out To The Web

React is primarily a library for building user interfaces. However, it’s important to note that it doesn’t provide built-in ways to connect to a web server and retrieve or manipulate data. Instead, this is typically done through third-party libraries like Axios.

HTTP Requests in a Single Page Application

In a single page application (SPA), the browser communicates with the server via HTTP requests, usually returning JSON data rather than HTML pages. The SPA updates its user interface based on this data, without requiring a full page refresh.

You can use the XMLHttpRequest object built into JavaScript for making HTTP requests. But as this can get cumbersome, libraries like Axios are often used instead. Axios is a promise-based HTTP client that works well in JavaScript environments including React.

Axios can be used in the componentDidMount() lifecycle method in class components or useEffect hook in functional components. Since HTTP requests are asynchronous, Axios returns a Promise that resolves to the response from the server.

Routing in React

React doesn’t have built-in support for routing, but libraries like React Router can be used. Routing is the process of selecting a path for traffic in a network or between or across multiple networks.

React Router keeps your UI in sync with the URL. It features intuitive, declarative routing and doesn’t reload the page during navigation. The two main types of components in React Router are router components and route matching components. Routers determine your application’s routing region, and route matching components show and hide your UI.

Code Splitting / Lazy Loading

In large React applications, it can be beneficial to split the code into separate bundles and load them on demand, a technique known as code splitting or lazy loading. This can greatly improve the initial load time of your application.

React supports code splitting through the dynamic import() syntax. It allows you to split your code into small chunks which you can then load on demand. React.lazy function lets you render a dynamic import as a regular component. It automatically loads the bundle containing the OtherComponent when the component gets rendered.

When Deploying Your APP on the Web with Routing

While deploying a React app with routing, it’s important to ensure that the server is configured correctly. Since all routes are managed on the client side with React Router, the server needs to be configured to always serve the index.html file, which bootstraps the React application, regardless of the requested route.

Understanding State

State in React components determines the components’ behavior and rendering. It’s an integral part of every React component that can “contain” data that may change over time and affect the rendering of the component.

Redux is a predictable state container designed to help you write JavaScript apps that behave consistently across client, server, and native environments. It helps you manage global state in bigger JavaScript apps.

How Does Redux Work?

Redux works by having a central store that holds the entire state of the application. Each component can access the stored state without having to send down props from one component to another.

There are three building parts: actions, store, and reducers.

Actions are events. They send data from your application to your Redux store. The data can be from user interactions, API calls, or even form submissions.
Reducers decide how the application’s state changes to an action. Reducers are pure functions that take the current state of an application, perform an action, and return a new state.
Store is the object that brings actions and reducers together. The store has several responsibilities: holds the application state, allows access to the state via getState(), allows state to be updated via dispatch(action), registers listeners via subscribe(listener), and handles unregistering of listeners.

Types of State

Determining what state should live inside Redux and what state should live inside React components can be challenging.

Local UI State: This is the state that is local to a particular component and doesn’t impact the rest of the app. This includes things like form input values, the open/closed status of UI elements like dropdowns, or temporary UI state like spinners and toasts. These types of state are usually best managed inside the component itself using React’s built-in state handling capabilities.
Persistent State: This type of state is data that is persisted on the server and needs to be fetched and updated via API calls. Examples of this type of state include the data displayed in lists or tables, the current user’s information, etc. This state is typically managed via Redux, often in conjunction with middleware like redux-thunk or redux-saga that can handle the asynchronous nature of API calls.
Client State: This is state that is global to the client application and may impact multiple components across the app. This includes things like user authentication status, selected values that may impact multiple components, UI themes, etc. This type of state is also often managed with Redux, since it allows for a consistent, predictable state management paradigm across the app.

Redux’s global state management can be particularly beneficial in larger apps where state needs to be shared across multiple components or where state management becomes more complex. However, for smaller apps, using React’s built-in state can often be simpler and faster to implement.

It’s also important to note that Redux is not the only solution for state management in React apps. Other options include the Context API and libraries like MobX and Zustand. The choice of state management tool will depend on the specific requirements of your app and your own personal preference.

Middleware

So, let’s talk about middleware in Redux. Imagine you’re throwing a party. Your guests are your actions and the party itself is your reducer. Now, middleware is that cool DJ you’ve hired to keep the party going. The DJ doesn’t stop any guests from getting to the party, they just add a little something extra to keep the night interesting. That’s middleware for you, jazzing things up after your actions are dispatched but before they hit your reducer.

Authentication

As we move on to authentication in React, you’ve probably used cookies before, right? Well, single-page applications (SPAs) like React throw that out the window. Instead of a server giving you a cookie to remember who you are, SPAs get a token from the server after sending it your login details. This token is then stored and sent back to the server whenever you want to do something that needs verification, like changing a password. Only tokens made by the server will be accepted by the server – it’s like an exclusive club, you can’t just make your own membership card!

Testing

Now, when we talk about testing a React app, it’s not just about clicking around and seeing what happens. Think of it as trying to escape a maze; it’s about developing a strategy, testing hypotheses and learning from your mistakes. We use automated tests to do this effectively and efficiently, testing tiny parts of our app (unit tests), or bigger sections, to find and fix errors.

In terms of tools, Jest and Enzyme are your best friends for testing. Jest is like the organizer of the test: it sets up the tests, runs them and checks the results. Enzyme, on the other hand, is like the actor pretending to be your app, mimicking how it mounts components and creates the DOM tree.

When deciding what to test, it’s important to focus on the crucial parts of your app. Don’t waste time testing stuff like third-party libraries. Instead, focus on isolated units and see what happens when the properties in your components change. That’s where you’ll find the juicy bugs!

Deployment

When it’s time to show the world your creation, you’ll need to deploy your React app. It’s a pretty simple process, though it might seem intimidating at first. You’ll first need to adjust your base path (if you’re using React Router), and then run the command ‘npm run build’ to optimize your project. Your server should always serve the ‘index.html’ file, even if it can’t find a particular route. Finally, you upload the build files to a web server. That’s it – your app is now live and ready for the world to see!

Conclusion

To wrap it all up, developing an application using React is like embarking on an exciting journey. From creating your first component to deploying your app, you’ll face challenges but each one will offer a unique learning experience. Understanding concepts like middleware, authentication, and testing will not only equip you with the tools to build robust applications but will also prepare you to tackle complex problems. So keep learning, keep building, and most importantly, keep enjoying the process!