HTML5 Developer Interview Questions For 5 Years Of Experience

Web Workers are a browser feature that allows you to run JavaScript code in the background, separate from the main browser thread. They enable concurrent execution and help prevent blocking the user interface during computationally intensive or time-consuming tasks. Here are some key points about web workers: 1. Background Execution: Web Workers allow you to run scripts in the background without blocking the main thread. This keeps the user interface responsive and improves overall performance. 2. Separate Thread: Web Workers run in a separate thread from the main JavaScript thread, often referred to as the "worker thread." This thread is isolated and doesn't share the same memory space as the main thread. 3. Communication: Web Workers communicate with the main thread using messaging. They can receive messages from the main thread and post messages back to it. This messaging system allows data exchange and coordination between the worker and the main thread. 4. Limited Scope: Web Workers have limited access to browser APIs and the DOM. They can't directly manipulate the DOM or access certain objects and methods available in the main thread. This limitation helps maintain security and prevents worker threads from interfering with the user interface. 5. Types of Web Workers: There are two types of web workers: dedicated workers and shared workers. Dedicated workers are tied to a specific script and can communicate only with the script that created them. Shared workers can be accessed by multiple scripts or web pages running on the same origin, allowing them to share data and communicate with multiple sources. Web Workers are useful for various tasks such as heavy computations, parsing large datasets, performing complex algorithms, and offloading non-UI tasks. They can help improve the overall responsiveness and performance of web applications by distributing the workload across multiple threads. Here's a simple example of using a web worker: 

// main.js (main thread)
const worker = new Worker('worker.js');

worker.onmessage = function(event) {
  console.log('Message from web worker:', event.data);
};

worker.postMessage('Hello from main thread!');


// worker.js (worker thread)
self.onmessage = function(event) {
  console.log('Message from main thread:', event.data);
  self.postMessage('Hello from web worker!');
};
In this example, the main thread creates a web worker using the `Worker` constructor, specifying the script file (`worker.js`). The main thread sends a message to the web worker using `worker.postMessage()`. The web worker receives the message in its `onmessage` event handler, logs it, and sends a response back to the main thread using `self.postMessage()`. The main thread receives the response in its `onmessage` event handler and logs it. Web Workers are supported in modern browsers and provide a powerful tool for performing background tasks, improving performance, and enhancing the user experience of web applications.
Accessibility is an essential aspect of web development, ensuring that websites and applications are usable by people with disabilities. Here are some important points related to accessibility: 1. Semantic HTML: Use appropriate HTML tags to convey the structure and meaning of the content. Use headings (`<h1>` to `<h6>`) to organize content, `<p>` for paragraphs, `<nav>` for navigation sections, `<button>` for interactive buttons, etc. This helps screen readers and assistive technologies understand the content and provide a better experience for users. 2. Keyboard Accessibility: Ensure that all functionality can be accessed and operated using a keyboard alone. This is crucial for people with motor disabilities who rely on keyboard navigation. Make sure focus is properly managed and visible, and elements such as buttons, links, and form inputs are keyboard accessible and provide appropriate feedback. 3. Alt Text for Images: Provide descriptive alternative text (`alt` attribute) for images. This allows screen readers to describe the content of images to visually impaired users. Use concise and meaningful descriptions that convey the purpose or information conveyed by the image. 4. Contrast and Color: Use sufficient contrast between text and background colors to ensure readability. Low contrast can make it difficult for people with visual impairments or color blindness to read content. Consider using tools to check contrast ratios and ensure compliance with accessibility standards. 5. Forms and Labels: Use proper form elements and labels to provide clear instructions and associations. Associate labels with form inputs using the `for` attribute or by wrapping the input within the label element. This helps screen readers understand the purpose of form inputs and improves usability for users with visual impairments. 6. Focus Indicators: Ensure that focus indicators are clearly visible and distinguishable. When users navigate through a page using the keyboard, it's important to provide a visual indication of the focused element. This helps users with disabilities understand their location within the page and improves overall navigation. 7. ARIA Roles and Attributes: Use ARIA (Accessible Rich Internet Applications) roles and attributes to enhance the accessibility of complex or custom UI components. ARIA attributes provide additional information to assistive technologies, helping them understand and navigate interactive elements like menus, tabs, and modals. 8. Responsive and Mobile Accessibility: Ensure that your website is responsive and works well on different devices and screen sizes. Consider the needs of users with disabilities who may access your site using mobile devices or assistive technologies. Test your site's accessibility on mobile devices and use media queries to adapt the layout and design. 9. Testing and Auditing: Regularly test and audit your website for accessibility. Use automated accessibility testing tools to identify common issues, and perform manual testing to understand the experience from the perspective of users with disabilities. Incorporate accessibility into your development process to catch and address issues early on. 10. Continuous Learning: Stay updated with accessibility guidelines and best practices. Accessibility standards and techniques evolve, so it's important to continuously learn and improve your understanding of accessibility to create inclusive and usable experiences for all users. These points highlight some important considerations for creating accessible websites and applications. By following accessibility best practices, you can ensure that your content is available and usable by a wider range of users, regardless of their abilities or disabilities. The WCAG 2.0 is organized in three different levels: Level A: the most basic Web accessibility features; Level AA: the most common barriers for disabled people; Level AAA: the highest level of accessibility. Even level A is just the beginning, and the level AA embraced on large companies’ websites, the level AAA is the one to which is hoping that someday all the Web products will go. For reaching those, it’s very important to have empathy for your users, they need to have excellent experiences on the Web, too.
The HTML <map> tag defines an image map. An image map is an image with clickable areas. The areas are defined with one or more <area> tags. HTML:- 

<img src="workplace.jpg" alt="Workplace" usemap="#workmap" width="400" height="379">

<map name="workmap">
  <area shape="rect" coords="34,44,270,350" alt="Computer" href="computer.htm">
  <area shape="rect" coords="290,172,333,250" alt="Phone" href="phone.htm">
  <area shape="circle" coords="337,300,44" alt="Cup of coffee" href="coffee.htm">
</map>
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A websocket is basically a connection between the client and the server in a way that server can send data to the client whenever it wants without waiting for the client to make a http request. A request to a WebSocket connection is sent to the server from a client (or multiple clients) through a process called the WebSocket handshake, which starts with the client sending a regular HTTP request to the server. Part of this request includes an Upgrade header, which indicates to the server that the the client is trying to make a WebSocket connection. This request is called a WebSocket handshake