Learn Eslint, Firebase and Radium

React is one of the web’s most popular frameworks for building JavaScript applications. 

If you know what you’re doing, React can drastically simplify how you build, use, and maintain code.

Whether you’re a React newbie or you’re ready for advanced techniques, you can level-up with egghead. Explore our in-depth courses, lessons, and community resources to build more powerful applications and crack open your career.

react

In a CSS library like Bootstrap we can set a button's style to be "primary" or "secondary" by appending classes. For React components we want to be able to do this via props. Radium enables this by composing styles via an array. This mimicks the cascade of CSS.  

Radium: Updating Button Styles via Props

React's inline styles allow components to stand on their own by not requiring any external CSS. However HTML's style attributes don't support pseudo selectors like `:hover` and `:active`. By using Radium to listen to mouse events we can restore `:hover` and `:active` selectors to inline styles.

Styling a React button component with Radium

ESLint is a JavaScript linter (static analysis tool) that offers full support for ES6, JSX, and other modern tools via plugins. We walk through setting up ESLint in a project, using the `eslint --init` CLI tool with the JSX and ES6 options, writing a React component in JSX, and adding some extra react linting rules with a plugin. ESLint is built to be "pluggable" with simple, extendable, modular rules and an API for writing and using plugins. ESLint has many rules which are all turned off by default; you can extend the core "recommended" rules which will catch common JavaScript errors, and you can also turn on stylistic rules for code consistency. You can also use plugin rules which we do in this lesson with the `eslint-plugin-react` package.

Linting React JSX with ESLint (in ES6)

AngularJS is an open-source JavaScript framework, maintained by Google, that assists with running single-page applications. Its goal is to augment web-based applications with model–view–controller (MVC) capability, in an effort to make both development and testing easier.

angularjs

The Firebase Forge provides a convenient GUI for visualizing and manipulating your data in real-time. Be sure to check out [this lesson](https://egghead.io/lessons/angularjs-get-started-with-firebase-and-angularfire) for getting Firebase setup.

Updating Real-Time Data with Firebase Forge

When using Firebase collections in your AngularJS application, you have access to a handy set of events emitted by the collection when changes in your data occur. Be sure to check out the [first lesson](https://egghead.io/lessons/angularjs-get-started-with-firebase-and-angularfire) in this series for the project source code.

Firebase Event Handling

Firebase provides a real-time syncing backend for your AngularJS applications in very few lines of code. In this lesson, you'll learn how to get started integrating it into your app.

Get Started with Firebase and AngularFire

Data has relationships, and Firebase allows you to define those relationships in your AngularJS applications.

Firebase Data Relationships

Firebase has several ways to provide authentication for your AngularJS application. In this lesson, Lukas will look at the most basic email/password approach.

Firebase Basic Authentication Part 1

Nuclide is the IDE Facebook employees use to write React code. But setting it up to use Flow type checking and Eslint to lint files on the fly is tricky. This video shows you how. 

Setup Nuclide to use Flow and Eslint (Mac)

React becomes incredibly powerful when coupled with a real-time backend like Firebase. See how easy it is to bring the two together and chat with Star Wars characters while you're at it.

React and Firebase with ReactFire

The pluggable linting utility for JavaScript and JSX.

eslint

ESLint is a JavaScript linter (static analysis tool) that offers full support for ES6, JSX, and other modern tools via plugins. We walk through setting up ESLint in a project, using the "init" CLI tool, configuring warnings/errors for rules, and adding editor plugins and build integrations. ESLint is built to be "pluggable" with simple, extendable, modular rules and an API for writing and using plugins. ESLint has many rules which are all turned off by default; you can extend the core "recommended" rules which will catch common JavaScript errors, and you can also turn on stylistic rules for code consistency.

Linting JavaScript with ESLint

Authenticating with Firebase creates a 24 hour session for the user. This allows you to fetch the current session for the user, as well as logout the user and destroy the session.

Firebase Basic Authentication Part 2

JavaScript is great! JavaScript is also full of features and flexible options that can make it easy to introduce bugs. ESLint uses static analysis to check that your code adheres to a list of rules to help you avoid some specific runtime errors. ESLint is highly configurable, so in this lesson, we'll install ESLint and configure some baseline rules for our boilerplate.

Avoid Common JavaScript Errors with ESLint 

Our first layer of defense when building accessible React applications is to add some auditing tools to our development workflow. This should include adding static analysis checking for common accessibility standards and best practices. We can get this with the latest eslint plugin: "eslint-plugin-jsx-a11y". If you are already linting your projects adding this plugin should fit very smoothly into your workflow.

## Resources
1. [List of all the rules supported by eslint-plugin-jsx-a11y](https://github.com/evcohen/eslint-plugin-jsx-a11y#supported-rules)
2. [Comparison of the difference in rules between recommended and strict mode](https://github.com/evcohen/eslint-plugin-jsx-a11y#difference-between-recommended-and-strict-mode)
3. [Background on how the Accessibility API implemented by browsers interfaces with Assistive Technologies](https://github.com/evcohen/eslint-plugin-jsx-a11y#some-background-on-wai-aria-the-ax-tree-and-browsers)

Set up ESLint to Audit Accessibility Issues in React

We have a number of options to use when testing for accessibility issues concerning alternative text for images.  The react-axe library and axe browser extension will both report when an image is missing alternative text.  The tota11y browser extension will annotate any images that are missing alternative text.  Running eslint with the eslint-plugin-jsx-a11y plugin installed will report on any `<img>` elements missing an `alt` attribute.  Finally, we can use a screen reader to actually hear what is read when an image has focus.

Test for Image Alternative Text Accessibility Issues

Images must have text alternatives that describe the information or function 
represented by them so they can be read and understood by those using screen readers.

## Alternative text for images
* All `<img>` elements should have an `alt` attribute provided
    * When not provided many screen readers will fallback to reading the file name instead
* The `alt` value should not include words like _“image”_, _“picture”_ or _“icon”_
    * Screen readers are already announcing that the element is an image
* Images that are decorative only and provide no information or function to the page should be hidden from Assistive Technologies by providing an empty `alt` attribute (`alt=””`)

## References
* https://www.w3.org/WAI/tutorials/images/
* https://www.w3.org/WAI/tutorials/images/decision-tree/
* https://www.w3.org/WAI/tutorials/images/tips/
* https://www.w3.org/WAI/tutorials/images/informative/
* https://www.w3.org/WAI/tutorials/images/functional/
* https://www.w3.org/WAI/tutorials/images/textual/

Define Images with Appropriate Text Alternatives

Our accessibility auditing toolkit makes it very easy for us to test for any form controls that are missing labels or are not correctly associated with their labels.  Running Eslint with the eslint-plugin-jsx-a11y installed will show us any form controls with missing or unassociated labels.  Running react-axe or using axe to audit a web page will similarly list any of these findings.  Finally using tota11y we can annotate any form controls on a page that are missing labels.  This is definitely some of the lower hanging fruit that we can easily find and fix when making our applications accessible!

Test for Form Control Label Accessibility Issues

Labeling inputs, elements, and widgets add context and clarity for assistive technology such as screen readers.  Elements of a `<form>` such as `<input>` or `<textarea>` or `<select>` should be labelled by using a `<label>` element.  Placeholder text can be used in addition to a label but should not be used in place of a label as not all assistive technologies respect placeholder text.

Ensure Form Controls have Accessible Labels

JavaScript® (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, most known as the scripting language for Web pages, but used in many non-browser environments as well such as node.js or Apache CouchDB. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

javascript

In this lesson you will learn how to use the eslint yeoman generator to scaffold a new plugin to provide custom rules for your project. 
You will also be able to check the basic skeleton for an eslint ruleand a working example rule to apply a naming convention for async functions.

Scaffold an eslint Plugin with Yeoman

Nx already comes with a default TypeScript setup. Although you can opt-out of that and generate plain JS based components, especially in a large setup TypeScript can be beneficial in uncovering potential issues early. To add an extra level, Nx also comes with preconfigured eslint for all the apps and libraries. In this lesson we're going to explore the lint setup and how it can be used.

Linting a React app with Nx

🔥 Firebase provides several easy-to-use authentication methods that we can use to handle auth in React apps. 

In this lesson, we will cover how to authenticate a user via an email and password. This is done using `createUserWithEmailAndPassword` function available to us from the `firebase` library. 

You'll need firebase configured in your application which you can [read about here.](https://dev.to/farazamiruddin/react-firebase-add-firebase-to-a-react-app-4nc9)

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