Learn Eslint, Leaflet and Particle

If you've ever worked on a website for a business, there's a good chance you've included a map.

A Google Map embed is sufficient for showing a location, but doesn't leave you many customization options.

React Leaflet to the rescue!

In this course, Colby Fayock will guide you through a series of lessons and challenges that will build your map making skills as you build out a web app for a fictional restaurant.

You'll get practice with handling API keys and using React Hooks to implement a custom interactive map complete with metadata and additional overlays.

This course has built-in challenges that you are encouraged to pause and work through, but feel free to just watch.

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

Build Maps with React Leaflet

In this collection, you'll learn the basics of creating a new map in your React application with React Leaflet. We'll walk through adding the map itself as well as adding markers with popups, different shapes, and increasingly complex features to your map!

Mapping with React Leaflet

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

In this lesson, you will learn how to add a map to your React application using React Leaflet. We will walk through importing and configuring the Map and TileLayer components from React Leaflet to set up the new map.

Create a New Map using React Leaflet

In this lesson, you will learn how to add a Marker and Popup component to a Map when using React Leaflet. We'll walk you through importing the components and adding each one to the Map. Additionally, we'll resolve an issue with loading marker images that's inherent to creating a new React Leaflet map in Create React App, which we'll fix by manually importing the image from Leaflet and configuring those images to the marker.

Add a React Leaflet Marker with a Popup to a Map

In this lesson, you will learn how to add the Polygon and Circle shape components to a Map when using React Leaflet. We'll walk you through importing both components, adding each component to the Map, and setting a unique color for each shape.

Add Shapes to a Map in React Leaflet

In this lesson, you'll learn how to style shapes on your map to change the look and feel using React Leaflet's API. We'll use React component props like color and weight on our shapes to change the colors and styles.

Style React Leaflet Shapes using Component Props

In this lesson, you'll learn how to use CSS to style and animate shapes on your React Leaflet map. We'll use the className prop to add a custom class and add CSS to customize our shapes.

Style and Animate a React Leaflet Shape with Custom CSS

In this lesson, you will learn how to use React hooks to interface with the Leaflet Map API in React Leaflet. We'll connect a ref to our Map component using the useRef hook and then use the useEffect hook to access that ref, find our Map instance, and use it to fly to a new location.

[More details on the Leaflet Map API](https://leafletjs.com/reference-1.6.0.html#map)

Interface with the React Leaflet Map API with the useRef and useEffect React Hooks

In this lesson, you learn how to use the React Leaflet ZoomControl component to add a custom zoom control to your map. We'll walk through removing the default control to avoid duplicates, using the ZoomControl position prop to change its location, and setting custom icons with the zoomInText and zoomOutText props.

Change the React Leaflet Map ZoomControl Location and Icons

In this lesson, you will learn how to add GeoJSON data to a map in React Leaflet. Using the National Parks in the United States, we'll import a GeoJSON document, create a new Leaflet GeoJSON instance, and add a marker with a popup for each park.

[Parks Locations Example](https://www.nps.gov/maps/tools/npmap.js/examples/geojson-layer/)
[Parks GeoJSON](https://www.nps.gov/lib/npmap.js/4.0.0/examples/data/national-parks.geojson)

Add GeoJSON Location Data to a Map Using Markers and Popups in React Leaflet

In this lesson, we'll add a new tile service as our basemap in React Leaflet. Using the NASA GIBS Blue Marble, we'll update the TileLayer component's url and attribution props to the new service. We'll also add the maxNativeZoom prop which allows us to configure the maximum zoom allowable for the service.

[More info about NASA GIBS imagery](https://earthdata.nasa.gov/eosdis/science-system-description/eosdis-components/gibs)
[GIBS Imagery API](https://wiki.earthdata.nasa.gov/display/GIBS/GIBS+Available+Imagery+Products)

### NASA GIBS Blue Marble Tile Server
Endpoint: https://gibs-{s}.earthdata.nasa.gov/wmts/epsg3857/best/BlueMarble_ShadedRelief_Bathymetry/default//EPSG3857_500m/{z}/{y}/{x}.jpeg
Attribution: NASA Blue Marble, image service by OpenGeo

Change the Map Tile Service of a React Leaflet TileLayer Basemap to NASA GIBS Blue Marble

In this lesson, we'll add a LayersControl toggle to allow us to change between multiple TileLayer basemaps in React Leaflet. Using the NASA GIBS Blue Marble, we'll add an additional TileLayer component, wrap our two TileLayers in BaseLayer components, and wrap all of our layers in a LayersControl to toggle our basemaps.

[More info about NASA GIBS imagery](https://earthdata.nasa.gov/eosdis/science-system-description/eosdis-components/gibs)
[GIBS Imagery API](https://wiki.earthdata.nasa.gov/display/GIBS/GIBS+Available+Imagery+Products)

### NASA GIBS Blue Marble Tile Server
Endpoint: https://gibs-{s}.earthdata.nasa.gov/wmts/epsg3857/best/BlueMarble_ShadedRelief_Bathymetry/default//EPSG3857_500m/{z}/{y}/{x}.jpeg
Attribution: &copy; NASA Blue Marble, image service by OpenGeo

Add a LayersControl Toggle to Switch Between TileLayer Basemaps in React Leaflet

In this lesson, we'll use the LayerGroup and FeatureGroup components to organize feature shapes on our map. Using these grouping features, we'll learn how the LayerGroup is used for organizational purposes like adding or removing multiple layers at once and how we can update the color of all of our grouped shapes with the color prop on our FeatureGroup.

Manage Map Data and Feature Shapes Together in a React Leaflet LayerGroup or FeatureGroup

In this lesson, we'll use an image to create a custom map marker icon for GeoJSON location data on our map. We'll walk through importing a custom image, creating a new Leaflet Icon and Marker instance, and use them to customize our National Parks markers.

Customize GeoJSON Data Markers with a React Leaflet Icon Image

In this lesson, we'll use the Leaflet setView and flyTo methods available on a map instance to change the location of a React Leaflet map. Using buttons to demonstrate, we'll walk through adding the setView method using a position and zoom level as well as the flyTo method which allows us to animate changing the location along with a specified duration.

Change the Location of a React Leaflet Map with Leaflet's flyTo and setView

In this lesson, we'll use geojson.io to add markers and draw shapes to create a GeoJSON document that we can add to our React Leaflet map. We'll walk through drawing the shapes, creating a new file to store the GeoJSON data, importing it to our app, and displaying it on our map with the React Leaflet GeoJSON component.

[Geojson.io](http://geojson.io/)
[Geojson.io Centered on Central Park](http://geojson.io/#map=16/40.7710/-73.9743)
[GeoJSON Spec](https://geojson.org/)

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