Learn Chrome-devtools, Clojure and D3

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 will learn and demonstrate the fundamental concepts and APIs of D3, on our way to building several common chart types. We’ll start with the building blocks upon which all D3 visualizations are built; things like scales, interpolators, and selections. We’ll see how to load data with D3, and how to put its full name, Data Driven Documents, into action. We’ll build column and bar charts, scatter plots, and area charts. Most importantly, we’ll gain an understanding of the conventions and patterns that underlie all D3 projects and examples, enabling you to dissect, understand, and build virtually any D3 visualization on the internet.

D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG and CSS. D3’s emphasis on web standards gives you the full capabilities of modern browsers without tying yourself to a proprietary framework, combining powerful visualization components and a data-driven approach to DOM manipulation.

Build Interactive JavaScript Charts with D3 v4

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 course covers D3 v3. If you'd like to learn about v4 of D3 (the latest version) [click here for the course on that](https://egghead.io/courses/build-interactive-javascript-charts-with-d3-v4).

This series will gently guide you through the first steps in getting to know D3. The curve can be steep, but with a few simple tools, you'll be charting your buns off in no time flat.

Use D3 (v3) to Build Interactive Charts with JavaScript

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

Clojure is a dynamic, general-purpose programming language, combining the approachability and interactive development of a scripting language with an efficient and robust infrastructure for multithreaded programming. Clojure is a compiled language, yet remains completely dynamic – every feature supported by Clojure is supported at runtime. Clojure provides easy access to the Java frameworks, with optional type hints and type inference, to ensure that calls to Java can avoid reflection.

clojure

In this lesson I show what a Clojure keyword is and why we prefer them as keys in maps; and the three ways we can look up a value in a map.

Keywords and Map Lookup in Clojure and ClojureScript

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/)

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