Learn Chrome, Ember and Mocha

Optional chaining ?. in javascript is a new feature introduced in ES2020. Optional chaining changes the way properties are accessed from deeply nested objects. It fixes the problem of having to do multiple null checks when accessing long chain of object properties in javascript.

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

Optional Chaining

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

 AJAX allows us to send requests to the server from our javascript applications, rather than allowing the browser to directly request declaratively specified resources. Under the hood, though, AJAX requests are still just HTTP requests - and that means we can use the Network Panel in Chrome’s DevTools to inspect our AJAX operations!


Examine AJAX Requests with Chrome Devtools

To understand the Network DevTool, you have to understand what HTTP is and how it works. Let’s use the Network DevTool to inspect an HTTP request and its corresponding response so that we can understand what the browser is doing.

Analyze HTTP Requests and Responses with Chrome Devtools

Most of today’s websites use optimized, compiled, minified and obfuscated javascript and CSS. Examining this stuff here has some severely limited utility, which is why when developing we rely on sourcemaps. We’ll set up a webpack workflow that uses sourcemaps to show you how they can help your debugging!

Unbundle your JavaScript with Source Maps in Chrome DevTools

Learn to use the Style panel within the Element Inspector to examine and tweak the CSS rules applied to your application as it runs. 

Chrome Devtools: Elements - Debug with Style!

The Element Inspector in Chrome DevTools offers powerful integration with the console - learn how to programmatically navigate your selected element, how to search through the history and use CSS selectors to control what you're looking at and how to quickly and easily listen for events as you debug your application.

Chrome Devtools: Elements - Console Integration

Use the Event Listeners tab within the Elements panel to list all DOM Event listeners. This is useful to understand how and why your site is reacting to various forms of input.

Understand the Event Listeners Panel

The Elements panel includes a tool to show you how your site will look across a variety of devices. This can be tremendously helpful when troubleshooting layout issues on specific hardware that you don’t have access to, as well as general-purpose response design. You can mock different screen resolutions and behaviors to help put you into your users’ shoes.

Use the Device Toolbar to Emulate Different Screens

There are a variety of ways to trigger the javascript debugger. Use the elements panel to set breakpoints on DOM elements so that you can hit the debugger whenever an element’s children or attributes change, or when it’s removed.

Use DOM Break Points

Using the Snippets tab in the source devtool you can define and run arbitrary pieces of code in your browser against whatever website you’re looking at. This is a great way to store commonly used pieces of code that you rely on for debugging or customization.

Use Snippets to Store Behaviors in Chrome DevTools

There are a variety of ways to trigger the debugger in Chrome's DevTools. You can set breakpoints on line numbers, break on XHR requests or DOM changes, break on specific events or even manually break by using the special `debugger` keyword in your code.

Set Breakpoints for the Chrome Debugger

Use the Chrome Debugger to pause execution of your application as it runs to see what’s happening in slow-motion. The debugger is an advanced tool that allows you to examine every change that happens in your application so that you can understand how and why your application state evolves over time.

Examine a Running App with the Chrome Debugger

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

Using the Chrome console, you can access your AngularJS injectable services. This is down and dirty debugging, and can be a lifesaver in troubling times.

Accessing Services from Console

A JavaScript framework for creating ambitious web applications.

ember

In this lesson we will create an `updateContent` method that sets the value of our `content` property to the current epoch timestamp. We need to call `toString()` on the `Date.now()` method in order to make TypeScript happy.

```
updateContent() {
  this.content = Date.now().toString()
}
```

We create a constructor that takes the options parameter, call `super(options)` and call into our `this.updateContent()` method.

```
constructor(options) {
  super(options)
  this.updateContent()
}
```

When we refresh our page we can see that the value of `content` is set to the epoch timestamp. 

To make the content really dynamic we use `setInterval()` to call into `updateContent` each second: `setInterval(() => this.updateContent(), 1000)`.

When we save our file we see that our content does not get updated anymore and when we check the console we see that we get an error telling us that: The 'content' property on the my-component component was changed after it had been rendered. The error also informs us that we should Use the @tracked decorator to mark this as a tracked property.

We add the @tracked decorator to our property, we import tracked from @glimmer/component and we refresh the page. We verify that `content` gets updated each second.

We change our `updateContent` to add our the timestamp to the array. When we use `this.items.push(this.content)` to achieve this we see that the list does not get updated. This is because the `@tracked` decorator only tracks the re-assignment of properties.

The way to get this working is by re-assigning our `items` array inside `updateContent`. We assign a new array, de-structure the current items array and add the new content.

```
this.items = [...this.items, this.content]
```



Use dynamic data in a GlimmerJS component

Cascading Style Sheets bring order and beauty to our applications.

In this lesson, we will create a fluid loading animation using Animations and Transformations in CSS3.

Summary:
1. Use keyframes to animate.
2. Add animation property to the required division.
3. Add in an appropriate Transition time.
4. Play with the easing function to get a smooth animation.

Build a Fluid Loading Animation in CSS

Learn how to use the Elements panel in chrome devtools to make structural changes to the DOM as it runs - you can explore what your site would look like with different elements and attribute values, all without polluting your source code.

Chrome Devtools: Elements - Make Changes in Your Browser

A large enough project will frequently flood the network devtool with content. Use the filter tool to restrict which HTTP requests you’re inspecting so that you don’t get overwhelmed.

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