Learn Chrome-devtools, Json-server and Nightmare

Frontend runtime optimization is heavily impacted by rendering.  Understanding the way the JS engine and the browser work is crucial for optimizing applications and understading how to avoid performance pitfalls.
This collection explains about the Critical Rendering Path, performance bottlenecks and practical solutions.

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

Critical Rendering Path

Chrome DevTools are incredibly useful for a frontend developer, sometimes we spend more time using them than our text editor of choice.

That's why it's so important to understand this tool better - those quick lessons will teach you things that will help you to become a more effective developer.

You will learn how to:

- **Use (experimental) CSS Overview to learn all about CSS used on a page in a minute**
- **Style console.log messages with CSS** - a _crucial_ skill for any senior developer (j/k)
- **Debug your code (on production and local environment) with logpoints**
- **Run a Lighthouse audit of your site**
- **Choose accessible colors for your website that have an AAA contrast ratio rating**
- **Force a DOM element state in Chrome DevTools**
- **Use Console utilities to make debugging easier**
- **Copy a network request as fetch or cURL with Chrome DevTools**

Have fun!

The Chrome Developer Tools (DevTools for short), are a set of web authoring and debugging tools built into Google Chrome.

chrome-devtools

Chrome DevTools tips & tricks

In this course we’ll take a deep look at the Elements panel in the chrome devtools. We’ll step through each button and tab on this panel and discuss how to use them to interact with your web application as it runs.

Debug the DOM in Chrome with the Devtools Elements Panel

This course examines the Sources panel in the Chrome DevTools, which allows you to see what files are responsible for the various things on the screen. Bundled into this panel, though, is the single most useful tool for any JavaScript developer - the JavaScript Debugger. We’ll use the Debugger to inspect JavaScript as it runs, allowing you to watch (and even interact with) the state of your application as it runs in ways that’ll blow your mind if you’ve mostly used console.log to debug your applications to this point. 

Debug JavaScript in Chrome with DevTool Sources

This course will examine the Network panel in Chrome DevTools. We’ll step through the request log, examining the various properties exposed. We’ll talk about timing, filtering, throttling and generally using the network panel to better understand the ways in which our applications exist within a connected context.

Debug HTTP with Chrome DevTools Network Panel

If you are developing JavaScript applications you are likely using logging as an integral part of your development process. Did you know that you aren't limited to simple `console.log` statements? Modern browsers give you a lot more logging options to work with!

This course will explore those options and give you some new logging tools for your professional toolbox.

Advanced Logging with the JavaScript Console

Miscellaneous one-off lessons on debugging, productivity hacks, and JavaScript tricks.

Tips and Tricks

This is a small collection of videos to help you get familiar with Chrome browser's performance oriented developer tools.
In this collection, learn how to record a performance profile, tweak the settings to get the most relevant profile and finally a look into the different sections of the performance data visualisation.

Basics of Chrome's Performance Devtools

Anything related to JavaScript performance

Javascript Performance

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

Progressive Web Apps can speed up app loading times, and even allow you to run your web app offline, and install it on a mobile device!  However, setting up a PWA correctly can be tricky.

In this course, we'll create a PWA from start to finish, using create-react-app.  We'll create a custom service worker, and use different caching strategies for different types of assets.

Finally, we'll look at how to install the app on both iOS and Android devices, and how to customize the app name, icon, and splash screen.

Course Introduction: Progressive Web Apps in React with create-react-app

Your page is showing high CPU usage and spinning up your laptop fan, but nothing is visibly happening. What is it doing, and why is it so slow?

This lesson is a real-world performance diagnosis of this very page, right here on egghead. Two infinite (but hidden) animations were causing CPU usage to spike, and Chrome's Task Manager and Performance tools helped uncover the elements causing the problem. You'll see how to use the profiler to record a snapshot, and learn a trick for discovering animations running in the background.

Diagnose a Slow Page Using Developer Tools

Sometimes we'd like to ensure that some `console.log` are *really* visible one someone opens dev tools window. For instance, we could want to warn our less tech-savvy users that they shouldn't paste anything someone else send them to console, because their account might get stolen.

In this lesson we are going to learn how to style `console.log` messages with CSS properties so we can make our messages stand out from the crowd.

Style console.log messages with CSS

What's in a name? In this lesson, I'll explain the concept of naming interactive elements for screen reader users, including forms, buttons, and links. You'll learn how to debug accessible names and descriptions using the Chrome Accessibility Developer Tools (previously a Canary experiment, now in Chrome), using multiple labeling techniques. We'll also listen to the effects of proper accessible names and descriptions in Voiceover and Safari.

For more information and the nitty-gritty browser implementation algorithm, refer to WAI-ARIA 1.1: 
- https://www.w3.org/TR/wai-aria-1.1/#namecalculation
- https://www.w3.org/TR/accname-1.1/

What is Accessible Name Calculation?

Chrome DevTools provide many handy utility functions that we can use to make debugging faster and easier so we can fix the bug and move on.

In this lesson we are going to learn how to use `$`, `$$` utilities built-in in Chrome DevTools to get references to single and many DOM elements and how to use `$0 - $4` variables to reference object selected using Inspect Element tool.

Use Chrome DevTools console utilities to make debugging easier

[Logpoints](https://developers.google.com/web/updates/2019/01/devtools) are one of the features recently released in Chrome 73. They allow you to easily log and debug your code (both on local environment and on production) without cluttering your code with `console.log()` statements everywhere and without using a debugger which might be an overkill when you simply want to log something.

In this lesson we are going to learn how to create Logpoints in Chrome DevTools to catch a bug in a JavaScript function.

Use Logpoints to log messages without cluttering up your code with console.log() statments

Choosing right colors for your website is difficult, especially when we want to develop accessible websites. Our goal should be to choose colors that have a high contrast ratio and as such can be easily read by all users, including those with low-vision impairments or color-vision deficiencies. 

In this lesson we're going to learn how to use Chrome DevTools Color Picker to choose colors for text which meet the [AA](https://www.w3.org/WAI/WCAG21/quickref/?versions=2.0#qr-visual-audio-contrast7) and [AAA](https://www.w3.org/WAI/WCAG21/quickref/?versions=2.0#qr-visual-audio-contrast7) contrast ratio score.

Choose accessible colors for text using Chrome DevTools Color Picker contrast ratio score

The Critical Rendering Path is what happens from the moment your javascript is running to the moment something changes on screen. In this lesson, we will see how to monitor and view the critical rendering path in the browser.

See the Critical Rendering Path in the browser

The axe browser extension (for Chrome and Firefox) is an immensely helpful tool for auditing web pages for accessibility defects.  This extension is powered by the same rules engine developed by Deque Labs in their axe-core open source library which also powers the react-axe development tool.  Each reported defect offers a ton of information about the defect, why it's a problem, severity level, groups impacted and ways to fix the defect.  This can be a great resource for learning more about how to write accessible code.

## Resources
* [Chrome browser extension](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd)
* [Firefox browser extension](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/)

Use the axe Browser Extension to Audit a Web Page for Accessibility Issues

Using our accessibility auditing toolkit we can find issues concerning landmark regions in our web application.  The react-axe library will report findings in the JavaScript console of the browser.  We could also run the axe browser extension to see the same results.  The tota11y browser extension will annotate any landmark regions on the page and therefore if none are annotated it may indicate that they aren't any (_NOTE: tota11y will only annotate landmark regions using aria roles and not those using HTML5 elements_).  Finally using the VoiceOver Rotor in Safari will show us whatever landmark regions have been defined in the Landmarks menu. 

Test for Landmark Region Accessibility Issues in React

When the contrast between foreground and background colors is not sufficient it can be hard to distinguish outlines, borders, edges, and details and text can be hard to read. The minimum recommended contrast ratio is 4.5:1 for most text. Very large text (120-150% larger than the default body text) can be slightly lower at 3:1. 

The contrast ratio of 4.5:1 was chosen because it compensates for the loss in contrast sensitivity usually experienced by users with vision loss equivalent to approximately 20/40 vision which is commonly reported as typical visual acuity of people at about age 80.

## References
* https://webaim.org/articles/contrast/
* https://webaim.org/resources/contrastchecker/
* [Accessible Color Picker Chrome browser extension](https://chrome.google.com/webstore/detail/accessible-color-picker/bgfhbflmeekopanooidljpnmnljdihld?hl=en-US)
* https://color.review/

Use Sufficient Color Contrast in Web Page Design

The pluggable linting utility for JavaScript and JSX.

eslint

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!

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