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A hook is just a function that conventionally starts with use. It can accept an arbitrary number of arguments, and return anything it wants. When exactly to add hooks instead of regular functions should be determined on a use case basis, and only experience will tell.
We start by forking the React template pen.
Here, every Button element has 2 props: We create 4 different buttons, with 4 increment values: When the button in the Button component is clicked, the incrementCount function is called. We use both in the incrementCount method implementation, which calls setCount updating the value to the existing value of count , plus the increment passed by each Button component.
The complete example code can be seen at https: Very simple example of a form that accepts a GitHub username and once it receives a submit event, it asks the GitHub API for the user information, and prints them.
This code creates a reusable Card component. When you enter a name in the input field managed by the Form component, this name is bound to its state. When Add card is pressed, the input form is cleared by clearing the userName state of the Form component. The example uses, in addition to React, the Axios library. Add it to the Pen settings in Codepen, or install it locally using npm install axios. We start by creating the Card component, the one that will display our image and details as gathered from GitHub.
It gets its data via props, using. We create a list of those components, which will be passed by a parent component in the cards prop to CardList , which simply iterates on it using map and outputs a list of cards:.
The parent component is App, which stores the cards array in its own state, managed using the useState Hook:. We must have a way now to ask GitHub for the details of a single username.
When the form is submitted we call the handleSubmit event, and after the network call we call props. We add it to App , passing a method to add a new card to the list of cards, addNewCard , as its onSubmit prop:.
Every time a CSS property has a dash, remove it and start the next word capitalized. CSS Modules seem to be a perfect spot in the middle: Start by creating a CSS file that ends with. A great choice is to give it the same name as the component you are going to style.
In the resulting markup, React will generate a specific, unique class for each rendered component, and assign the CSS to that class, so that the CSS is not affecting other markup. When you build a React application using create-react-app , you have many options at your disposal when it comes to styling.
Styled Components allow you to write plain CSS in your components without worrying about class name collisions.
Simply install styled-components using npm or yarn:. With the styled object imported, you can now start creating Styled Components. Here's the first one:. We created it using a function of the styled object, called button in this case, and passing some CSS properties in a template literal.
Styled Components offer other functions you can use to create other components, not just button , like section , h1 , input and many others. Props instead of just being blindly passed down to the DOM can also be used to customize a component based on the prop value.
If you have one component and you want to create a similar one, just styled slightly differently, you can use extend:. You can use media queries, nesting and anything else you might need. This will continue, because Babel is now indispensable and has solved a big problem for everyone.
The problem that every Web Developer has surely had: Which is now supported by all modern browsers. By checking the ES6 Compatibility Table. So how should you deal with this problem? Enter Babel. Babel is a compiler: This must happen at build time, so you must setup a workflow that handles this for you.
Webpack is a common solution. Babel is easily installed using npm , locally in a project:. Since npm now comes with npx , locally installed CLI packages can run by typing the command in the project folder:.
To solve the problem we talked about in the introduction using arrow functions in every browser , we can run. If you don't have that file already, you just create a blank file, and put that content into it.
Given a large number of files, it generates a single file or a few files that run your app. There are lots of similarities in what those and Webpack can do, but the main difference is that those are known as task runners , while webpack was born as a module bundler. Webpack can be installed locally as well. By default, webpack starting from version 4 does not require any config if you respect these conventions:.
The regular expression targets any CSS file. In this example, css-loader interprets the import 'style. What kind of loaders are there? You can find the full list here. See the babel-loader options here. Plugins are like loaders, but on steroids. There are lots of plugins available. This mode introduced in webpack 4 sets the environment on which webpack works.
Webpack can be run from the command line manually if installed globally, but generally you write a script inside the package. Webpack can automatically rebuild the bundle when a change in your app happens, and keep listening for the next change.
One nice feature of the watch mode is that the bundle is only changed if the build has no errors. If there are errors, watch will keep listening for changes, and try to rebuild the bundle, but the current, working bundle is not affected by those problematic builds.
Webpack allows us to use images in a very convenient way, using the file-loader loader. Check the Image docs. Since webpack bundles the code, Source Maps are mandatory to get a reference to the original file that raised an error, for example.
React Tutorials and Courses
You tell webpack to generate source maps using the devtool property of the configuration:. Its strengths are:. Jest can be installed in any other project using Yarn:. Projects created with create-react-app have Jest installed and preconfigured out of the box, but adding Jest to any project is as easy as typing.
Open a math. Now create a math. Running yarn test results in Jest being run on all the test files it finds, and returning us the end result:.
Even more important, if you are writing a Unit Test , you should test the functionality of a function in isolation, not with all its baggage of things it touches. Using mocks, you can inspect if a module function has been called and which parameters were used, with:. Jest provides a convenient way to mock an entire package. Say you import mathjs. You can also use jest.
You can find pre-made mocks for popular libraries. For example this package https: Snapshot testing is a pretty cool feature offered by Jest. This is a simple test on the App component of a simple create-react-app application make sure you install react-test-renderer:.
If App changes, you get an error:. When using yarn test in create-react-app you are in watch mode , and from there you can press w and show more options:. If your change is intended, pressing u will update the failing snapshots, and make the test pass. You can also update the snapshot by running jest -u or jest --updateSnapshot outside of watch mode.
The easiest way to start with testing React components is doing snapshot testing, a testing technique that lets you test components in isolation. I assume you created a React app with create-react-app , which already comes with Jest installed, the testing package we'll need.
CodeSandbox is a great environment to try this out. Start with a React sandbox, and create an App. When CodeSandbox detects test files, it automatically runs them for you, and you can click the Tests button in the bottom of the view to show your test results:. If you skipped it, you can go back and read how we built it, but for easier reference I add it here again. We are going to use the react-testing-library , which is a great help as it allows us to inspect the output of every component and to apply events on them.
You can read more about it on https: We start by importing render and fireEvent from react-testing-library , two helpers. The first lets us render JSX. The second lets us emit events on a component. Buttons are used in the app to accept a click event and then they call a function passed to the onClickFunction prop. We add a count variable and we create a function that increments it:.
Now off to the actual tests. It shows 4 buttons and the result in the page. We can inspect each button and see if the result increases when we click them, clicking multiple times as well:. Check the code working on this CodeSandbox: The ecosystem around React is huge. Here I introduce you to 4 of the most popular projects based upon React: React Router, Redux, Next. Routing in a Single Page Application is the way to introduce some features to navigating the app through links, which are expected in normal web applications:.
Routing links together your application navigation with the navigation features offered by the browser: React Router offers a way to write your code so that it will show certain components of your app only if the route matches what you define. Which one to use is mainly dictated by the browsers you need to support. If you don't have to worry about older browsers, it's the recommended choice. Route components are responsible for showing - or hiding - the components they contain.
You import it from react-router-dom, and you use it to wrap all your app:. The Link component is used to trigger new routes. You import it from react-router-dom , and you can add the Link components to point at different routes, with the to attribute:. Check this example on Glitch: Notice the exact attribute. You can have a route respond to multiple paths simply using a regex, because path can be a regular expressions string:. Instead of specifying a component property on Route , you can set a render prop:.
The only requirement of an action object is having a type property, whose value is usually a string. In a simple app an action type can be defined as a string, as I did in the example in the previous lesson. A reducer is a pure function that calculates the next State Tree based on the previous State Tree, and the action dispatched. A pure function takes an input and returns an output without changing the input or anything else.
Thus, a reducer returns a completely new state tree object that substitutes the previous one.
Second, if you are building a publicly available website, you have a content SEO issue. The solution to both of those problems is server rendering , also called static pre-rendering. It provides a common structure that allows you to easily build a frontend React application, and transparently handle server-side rendering for you.
This is the only thing that Next. Create an empty pages folder, and run the command again, and Next. In the pages folder create an index. Simply put, pages are inside a pages folder, and the page URL is determined by the page file name. The filesystem is the pages API. As you can see, the HTML generated by the component is sent directly in the page source. The Next. If you point your browser to localhost: As you can see, also this page is server rendered.
Note how you did not have to restart the npm process to load the second page. Server rendering is very convenient in your first page load, for all the reasons we saw above, but when it comes to navigating inside the website, client-side rendering is key to speeding up the page load and improving the user experience.
Try linking the two pages above. Now go back to the browser and try this link. As you can see, the Contact page loads immediately, without a page refresh. If you now cmd-click the link, the same Contact page will open in a new tab, now server rendered.
A good use case for Next. A dynamic page is a page that has no fixed content, but instead display some data based on some parameters. You can use clean URLs without query parameters. Styles are scoped to the component, but you can also edit global styles adding global to the style element:.
A Next. At the beginning of this tutorial you created a package. The company behind Next. Of course they integrate both their products so you can deploy Next. You can set up multiple Next. Check out my Next. It is one of the tools that allow you to build on a set of technologies and practices collectively known as JAMstack. Gatsby is one of the cool kids in the Frontend Development space right now.
I think the reasons are:. All you need is a place that serves plain HTTP pages and your assets to the client. I mentioned Progressive Web Apps in the list. Gatsby automatically generates your site as a PWA, with a service worker that speeds up page loading and resource caching. This command creates a brand new Gatsby site in the mysite folder, using the starter available at https: A starter is a sample site that you can build upon.
Meet Wes Bos
Another common starter is default , available at https: The browser should instantly hot reload the component which means the page does not actually refresh, but the content changes - a trick made possible by the underlying technology. To add a second page, just create another. You can link those pages by importing a Gatsby-provided React component called Link:.
Gatsby provides lots of things out of the box, but many other functionalities are provided by plugins. A Gatsby plugin is installed in 2 steps. First you install it using npm , then you add it to the Gatsby configuration in gatsby-config. In gatsby-config.
14 Free React JS Books
Once you are done tweaking the site and you want to generate the production static site, you will call. Once you build the site using gatsby build , all you need to do is to deploy the result contained in the public folder. Here are some great guides for some popular hosting platforms where you can deploy Gatsby. I hope this book has helped you get started with React, and maybe it gave you a head start in exploring some of the most advanced aspects of React programming. Learn Forum News.
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CodeSandbox is a great way to start a React project without having to install it locally. Codepen Another great solution is Codepen. I will mention a list of things to get you up to speed quickly.
Taming the State in React
Variables A variable is a literal assigned to an identifier, so you can reference and use it later in the program. Using var Until ES, var was the only construct available for defining variables. Using let let is a new feature introduced in ES and it's essentially a block scoped version of var. Using const Variables declared with var or let can be changed later on in the program, and reassigned. Implicit return Arrow functions allow you to have an implicit return: It works when there is a one-line statement in the function body: When defined as a method of an object, in a regular function this refers to the object, so you can do: DOM Event listeners set this to be the target element, and if you rely on this in an event handler, a regular function is necessary: Clone an object with: The most important one is the ability to use an array as function argument in a very simple way: Rest properties: Tom, age: The syntax also works on arrays: The syntax at a first glance is very simple, just use backticks instead of single or double quotes: First Second an easy way to fix this problem is by having an empty first line, and appending the trim method right after the closing backtick, which will eliminate any space before the first character: A class definition This is how a class looks.
In this case hello is a method and can be called on all objects derived from this class: If the inherited class has a method with the same name as one of the classes higher in the hierarchy, the closest method takes precedence: I am a programmer.
Inside a class, you can reference the parent class calling super.
Static methods Normally methods are defined on the instance, not on the class. Static methods are executed on the class instead: Getters and setters You can add methods prefixed with get or set to create a getter and setter, which are two different pieces of code that are executed based on what you are doing: Asynchronous means that things can happen independently of the main program flow. Lines of code are executed in series, one after another, for example: This event handler accepts a function, which will be called when the event is triggered: One common example is by using timers: However every callback adds a level of nesting, and when you have lots of callbacks, the code starts to be complicated very quickly: How do we solve this?
How promises work, in brief Once a promise has been called, it will start in pending state. Consuming a promise In the last section, we introduced how a promise is created.
Chaining promises A promise can be returned to another promise, creating a chain of promises. Running fetch returns a response , which has many properties, and within those we reference: Handling errors In the above example, in the previous section, we had a catch that was appended to the chain of promises. Orchestrating promises with Promise. How it works An async function returns a promise, like in this example: Here's an example: This is why this code is valid: I did something and I watched and I watched as well Easier debugging Debugging promises is hard because the debugger will not step over asynchronous code.
For example, this module exports a function that returns a string uppercase: In a file however you can export more than one thing, by using this syntax: What does this mean?
Only very innovative products worked differently, and experimented with new approaches. Examples of Single Page Applications Some notable examples: Gmail Google Maps Facebook Twitter Google Drive Pros and cons of SPAs An SPA feels much faster to the user, because instead of waiting for the client-server communication to happen, and wait for the browser to re-render the page, you can now have instant feedback.
Overriding the navigation Since you get rid of the default browser navigation, URLs must be managed manually. Declarative What does it mean when you read that React is declarative? Immutability One concept you will likely meet when programming in React is immutability and its opposite, mutability. An immutable variable can never be changed. To update its value, you create a new variable. The same applies to objects and arrays. An object is never updated, but copied before changing it.
This applies to React in many places. In Redux, you never mutate the state directly, but only through reducers, which are functions. The question is, why? There are various reasons, the most important of which are: Mutations can be centralized, like in the case of Redux, which improves your debugging capabilities and reduces sources of errors.
Why Invest in Mobile Applications? Apple, on the other hand, claims to have passed the milestone of 1. What Are Native Apps? A native app a platform-specific code in the language dedicated to a given mobile OS. To develop a native app, programmers work on an Integrated Development Environment IDE specific for a given operating system. The most common way of delivering mobile applications is through native platforms.
Native apps offer ultra-fast performance, easy access to all device APIs and functionalities, and optimal responsiveness. If there are so many evident benefits of native apps, that raises a question: Why do mobile developers use React Native for mobile development instead of going fully native? This benefit is of prime value, as rapid code delivery allows businesses to gain a competitive edge by shipping innovative products first to the market.
Quicker Product Updates and Feature Extensions While testing and updating an app with React Native, the dev team also perform all tasks only once, which results in further time savings.
In a small team, each person assumes responsibility for their work, which motivates them and increases their engagement. The immediate, direct communication within the team leads to faster development and issue resolution.
Smaller teams are also much easier to manage. All of the code is organized into folders. Each folder starts with a number followed by the application name. For example, Chapter First of all, you need the latest version of a modern web browser, such as Google Chrome or Mozilla Firefox:.
React and React Native.
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Sign up for free See pricing for teams and enterprises. React 16 Essentials — Second Edition, published by Packt. Find File. Download ZIP. Sign in Sign up. Launching GitHub Desktop Go back.Here's the first one: In the current consumer computers, every program runs for a specific time slot, and then it stops its execution to let another program continue its execution. You can find pre-made mocks for popular libraries.
React Native allows them to perform changes, including error handling, at runtime, and immediately see the results of their work on the running app. This example puts the output bundle into app. You can also invoke the tests manually by selecting the Jest: Asynchronous means that things can happen independently of the main program flow.
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