Learn Eslint, React-router and Xstream

React Router v4 takes an entirely new approach to routing and handling URLs in your React applications. It fully embraces the concept of declarative programming and a component based development process. In practice, this turns out to be very nice and gives you a routing solution that is less configuration heavy than many previous solutions.

In this course, you will learn about the basics of React Router v4 to help you get started. We will look at the core components that React Router supplies and how they interact together to create a robust routing solution for your React applications.

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.

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Add routing to React apps using React Router v4

React Router is the defacto router for any React application and it allows us to extract the state of our application from the browser's address bar.

In this course we'll explore the core features of React Router in common examples.  From routing with individual components to more complex routing consisting of multiple components, query-strings, route parameters,  and redirects.  

Getting Started with React Router v3

Routes are some times better served as a modal. If you have a modal (like a login modal) that needs to be routeable and appear on all pages you may need to use query params. Will explore how to render a route all the time and use query params to control when it's content renders

Create a Query Parameter Modal Route with React Router

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

The pluggable linting utility for JavaScript and JSX.

eslint

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

Gatsby is a blazing fast static site generator built with React. Gatsby gives you all of the modern JavaScript tools you want; set up and ready to go out of the box.

gatsby

Restricting access to content that is delivered client-side in a Gatsby site takes a few steps. We use Netlify Identity to handle user authentication and reach router to build our auth-restricted client-side application.

Using Netlify Identity to control access to a Gatsby client-side dashboard route

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.

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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

React Router v4 doesn’t require a lot of configuration to run. The core examples will run out of the box with Create React App. In this lesson, you will create an application and get React Router v4 up and running.

_**note**: in this video `react-router-dom` is installed with the `--save-dev` flag. This is **not required and may cause issues if used**. Simply install it with `npm install react-router-dom` and it will function as expected._

Run the React Router v4 Examples with Create React App

React Router 4 has several routers built in for different purposes. The primary one you will use for building web applications is the BrowserRouter. In this lesson you will import the BrowserRouter and create some basic Route components.

Create Basic Routes with the React Router v4 BrowserRouter

setRouteWillLeaveHook provides a method for us to intercept a route change before leaving the current route.

React Router: setRouteWillLeaveHook

React-router is the community favourite routing solution - it can handle all of your complex routing needs and in this lesson we’ll cover what’s needed to enable it’s use within Preact. https://github.com/ReactTraining/react-router

Integrate react-router with Preact

IndexRoute allows us to define a default child component to be rendered at a specific route when no other sub-route is available.

React Router: IndexRoute

We can use regular expressions to more precisely define the paths to our routes in React Router v4.

Use Regular Expressions with Routes with React Router v4

In this lesson we'll look at hashHistory which uses a hash hack to track our route changes vs browserHistory which delivers clean urls, but requires server work to implement

React Router: hashHistory vs browserHistory

Since react-router routes are components, creating nested routes is as simple as making one route a child of another in JSX.  In this lesson we'll explore nesting routes and accessing the children of parent routes.

React Router: Nested Routes

A router library is no good if we have to hardcode every single route in our application.  In this lesson we look at how to access variables in our routes and pass them into our components.

React Router: Route Parameters

In this lesson we'll learn how to render multiple component children from a single route.

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