Sample Answer
The CSS box model is a rectangular design concept that encapsulates each HTML element. It consists of four areas – the content area, padding area, border area, and margin area, listed in order from innermost to outermost. The content area contains the actual content of the element like text or images. The padding area is the space between the content and the border. The border area is self-explanatory – it’s the border surrounding the padding and content areas. The margin area is the space around the border. The box model is fundamental in CSS because it determines how elements interact with each other in terms of space and layout.

Sample Answer
‘==’ checks for equality with coercion. This means it checks if the values are equal after attempting to convert them to a common type. For example, when comparing a string and a number, the string will be converted to a number before the comparison. On the other hand, ‘===’ checks for equality without coercion, meaning it checks both the value and the type. So, if you compare a string and a number, even if the string is numerically equal to the number, the comparison will return false because the types are different.

Sample Answer
In JavaScript, a closure is a function that has access to its own scope, the outer function’s scope, and the global scope. This means that a function created inside another function has access to the outer function’s variables. Here’s an example:

function outerFunction(outerVariable) {
return function innerFunction(innerVariable) {
console.log(‘outerVariable:’, outerVariable);
console.log(‘innerVariable:’, innerVariable);
}
}
const newFunction = outerFunction(‘outside’);
newFunction(‘inside’);

In this example, outerFunction is the outer function and innerFunction is the closure. The newFunction can access variables from both the innerFunction and outerFunction scopes.

Sample Answer
‘Props’ in React are short for properties. They are a way of passing data from parent components to child components. The data being passed can be any JS type, including numbers, strings, objects, arrays, and even functions. The key thing to remember about props is that they are read-only. This means that a child component cannot change the value received from the parent component. Here’s a simple example:

function Welcome(props) {
return

Hello, {props.name}

;
}

In this example, the ‘Welcome’ component receives ‘props’ as an argument and uses it to display the name passed to it from the parent component.

Sample Answer
Frequent DOM manipulations can be a performance bottleneck as they trigger reflows and repaints. To handle this, I would use techniques such as debouncing, where I would batch multiple changes and apply them at once to minimize the number of reflows. Another approach is to use a virtual DOM, like the one React uses. A virtual DOM allows us to make changes to a light-weight copy of the actual DOM and then efficiently reconcile those changes with the real DOM.

Sample Answer
Scalable Vector Graphics, or SVGs, are an XML-based vector image format for two-dimensional graphics. Unlike other image formats like JPEGs or PNGs, SVGs are resolution-independent and can be scaled to any size without losing quality, which makes them perfect for responsive design. SVGs can be implemented directly into the HTML document, allowing them to be styled with CSS and manipulated with JavaScript. This means that you can change the color, size, position, and more, of an SVG image using code, which provides a lot of flexibility and interactivity.

Sample Answer
In my previous projects, I have encountered various browser compatibility issues. My approach is always to start by identifying the issue and the browsers that are affected. I use resources such as ‘Can I use’ to check browser support for certain features. I practice progressive enhancement, which focuses on basic content first and then progressively adds more nuanced and browser-specific features later. If a feature is not supported by a certain browser, I use feature detection with Modernizr to provide a fallback or use a polyfill to emulate the missing features. For example, in one of my projects, I had to use CSS Grid which wasn’t fully supported in some versions of IE. I used Modernizr to detect this and provided a fallback layout using Flexbox.

Sample Answer
CSS Preprocessors are scripting languages that extend the default capabilities of CSS. They enable us to use logic in our CSS code, such as variables, nesting, inheritance, mixins, functions, and mathematical operations, which can make our CSS more readable and easier to maintain. They are then compiled into regular CSS syntax that browsers can understand. Some examples of CSS Preprocessors are Sass, Less, and Stylus. In my previous projects, I have used Sass, which has made it easier for me to write reusable, maintainable and extensible code in CSS.

Sample Answer
A Promise in JavaScript represents a value that may not be available yet but will be resolved or rejected at some point in the future. It’s an object that can return a value which we can handle using .then() and .catch() methods. A Promise can be in one of three states: pending (the Promise’s outcome hasn’t yet been determined), fulfilled (the operation completed successfully), or rejected (the operation failed). Promises are often used to handle asynchronous operations, like API calls, where we have to wait for a response. An example of a Promise could be a function that fetches data from an API and returns a Promise that resolves to the data if the fetch was successful or rejects with an error if it wasn’t.

Sample Answer
Virtual DOM (VDOM) is a programming concept where an ideal, or “virtual”, representation of a UI is kept in memory and synced with the “real” DOM by a library such as ReactDOM. This process is called reconciliation. In React, when you render a JSX element, every single virtual DOM object gets updated. This sounds incredibly inefficient, but the cost is insignificant because the virtual DOM can update so quickly. When the virtual DOM gets updated, React compares the new virtual DOM with the old one and figures out what changes need to be made in the real DOM. This process of comparing the new virtual DOM with the old one is much faster than writing the new DOM. This is because writing on the virtual DOM in JavaScript is much faster than writing on the actual DOM. This ultimately improves the performance of the app and provides a better user experience.