HTML Document Object Model(DOM):Interview Questions and Answers
The Document Object Model or DOM is an important one for every web developer. It enables the users to control and create HTML and XML documents using any programming language. In case you are looking for a job in web development and an interviewer asks questions regarding the DOM, it would be wise to know what it is. In this article, we will look at some of the common questions in such interviews and their possible answers:
What is the DOM?
Question: What is the Document Object Model (DOM)?
Answer: The DOM is a structural component in the development of web documents. It organizes, or sees, the document as a tree in which each child has its own constituents: elements, attributes, text, or other information. This enables the authors to use several programming languages such as JavaScript to change or update any content, format or structure within web pages.
DOM Structure
Question: How is the DOM structured?
Answer: The document object model (DOM) has a tree structure having root under which other nodes of the elements of a document reside. Each individual element may be made to contain attributes and child nodes for construction of hierarchy. For example:
html
├── head
│ └── title
└── body
├── h1
└── p
DOM Methods
Question: What are some common methods to interact with the DOM?
Answer: There are different methods of Interacting with the DOM:
getElementById(id): Return an element with the specified ID.
getElementsByClassName(className): Return elements with the given class.
getElementsByTagName(tagName): Return elements with the given tag.
Modifying the DOM
Question: How can you modify the DOM using JavaScript?
Answer: You can also manipulate the DOM in a number of ways by doing the following actions:
Changing Content: Use innerHTML or textContent to modify what is in the element.
Adding Elements: Use createElement () to add new element and use appendChild() to fit it in the DOM.
Event Handling
Question: How does event handling work in the DOM?
Answer: Event handling in the DOM requires setting up listeners for user interactions, such as clicks or key presses. This can be achieved by using methods like addEventListener() to bind event listeners to specific elements.
Differences Between DOM and BOM
Question: What is the difference between the DOM and BOM?
Answer: The BOM (Browser Object Model) deals with interactions with the browser itself, offering access to features such as the browser window, history, and location.
Performance Considerations
Question:The DOM (Document Object Model) concentrates on the content of web documents, and allows for manipulating HTML and XML. The BOM (Browser Object Model), on the other hand, takes care of working with the browser as a whole including functionality like opening and closing new browser windows or managing history.
How does DOM Works?
Answer: For better performance when dealing with DOM, have in mind the following tips.
Reduce the Number of DOM Manipulations: Group states together instead of changing them one after another.
Avoid reflow and repaint issues due to adding multiple elements at once with Document Fragments.
Cache Selectors – Store refs to avoid mutliple dom selectors.
Advanced DOM Concepts
Question: Why use textContent over innerHTML?
Answer:
innerHTML : returns the HTML markup within an enclosed/provided element. This browser understands HTML and is scriptable, which makes it flexible. Though it is a little risky when user input involved, it may be candidate of xss attack
The textContent property sets does not parse HTML (unlike innerHTML) and makes it safe for user input handling.
What is event delegation and why is it essential?
Answer: Event Delegation is used for a single event listener in parent element which then listens events on multiple child elements. Such an approach is effective for it :
Performance: Reduces footprint of memory and increases performance due to not having numerous individual event listeners.
Delegates Events: It can automatically handle events of elements that may be created in the future without having to add event listeners again.
Question: What is a way to traverse the DOM?
Answer: You can identify all relevant properties to traverse the DOM.
parentNode : parentNode returns the parent of a specified node.
Child Nodes: childNodes returns a live NodeList of the child nodes.
First and last Child: The firstChild returns the first child node while lastChild returns the last child nodes.
Next and Previous Siblings: nextSibling / previousSibling – return to the following and previous siblings of nodes.
PreviousSibling return the next and previous nodes at the same tree level.
Question: What are data attributes in HTML and how we can access them via the DOM?
Answer: They are called custom data attributes because All of the metadata HTML elements provide but they did it themselves. The attribute name should start with date– to be used With the JavaScript we can access it by using the dataset property.
Question: Give a brief explanation of Virtual DOM
Shadow DOM: a web standard that helps you to encapsulate part of the DOM and its CSS, so it will not leak out to the main document. This is crucially important when it comes to building your own reusable components. The Shadow DOM provides:
Style Encapsulation: Styles declared within a Shadow DOM are contained and do not affect styles in the main document.
Encapsulation: Everything inside its shadow tree is shielded and cannot be accessed without, into the DOM.
Question: What does this document want to do? readyState property?
Answer: The document. Comment: readyState- current loading status of the document. These can have a handful of different values. The document has loaded fully and the user can now have interaction with it, but not all external resources like images are still been downloaded.
How to use this property, it can be used to run code when the page is fully loaded.
if (document.readyState === 'complete') {
// Execute code here
} else {
window.addEventListener('load', () => {
});
}
Javascript
if (document.readyState === 'complete') {
// Execute code here
} else {
window.addEventListener('load', () => {
});
}
Question: What is “Reflow’ and “Repaint”?
Answer:
Reflow: This happens when operations invoked via the JavaScript API alter the appearance of the page. It can occur when new or existing objects are incorporated or eliminated from the design or when size and content of objects are changed. Larger reflow is also expensive operation from performance point of view because the browser has check the style and layout again.
Repaint: This happens when modification does not re struct the format of the page but alters on aspects of the layout such as colour or visibility of some aspects of the page. Again, repainting is much cheaper than reflow, but repeated painting actually have similar effect on the previous option.
Advanced DOM Manipulation Techniques
Question: What is this concept, Document Fragment: what is its use?
Answer: Document Fragment is a domain object used for a lightweight container used to carry parts of the DOM tree. It is not in the main DOM tree, and this makes easy to manipulate it.
Question: How do you handle errors in the DOM?
Answer: We use try..catch blocks to avoid getting any exception occurring during DOM manipulations Possible improvements: A pop-up screen could be included at the end to allow for an overview or summary of the changes made then export the entire page in other formats such as PDF, etc. This is especially so when dealing with potential failure methods like compile, or querySelector on non-existent element.
Question: What’s the difference between Node, Element, and HTMLElement?
Answer:
Node: The loose class for all types of nodes, coming from elements, text nodes, and comment nodes.
Element: An extension of the Node class which embeds HTML or XML elements. It has its operations like properties for elements in the HTML document.
HTMLElement: It is an element subclass that contains all the objects of HTML documents containing different elements. There are properties unique to HTML elements, these include innerHTML, style, and attributes.
Question: What is the MutationObserver?
Answer: MutationObserver is a JavaScript object which is integrated by the browser to watch for changes in the DOM tree. For such modifications, it can watch for example added child nodes, attributes, and text content modification.
Question: Explain the concept of a "virtual DOM."
Answer: It is also called Virtual DOM which exists in libraries such as React; it is a copy of the DOM tree in the RAM. It is a replica of the actual DOM that will be created at run time. When changes happen, they happen to a virtual DOM first. A diffing algorithm can then calculate the minimum number of changes needed in order to arrive at the real DOM enhancing performance.
What is HTML?
HTML or hyper text markup language is the conventional language that is used globally to design documents for the web. It orders the contents of the page and is made of such components as those defined by tags – such as the angle brackets.
HTML or HyperText Markup Language is the most common programming language used to construct web pages. Here are some key features:
Elements and Tags: HTML employs tags known as elements within it to order content some of the elements include <p>, <h1>, <div>.
Attributes: It should be noted that tags can have attributes when creating which give extra information regarding class, id, and src.
Nested Structure: HTML able to have elements nested which organize the elements in forms of a hierarchy.
Semantic Elements: HTML5 has introduced many new tags including; <article>, <section>, <header>, <footer> which solved the problem of expressing the meaning of the content.
Forms and Input Elements: HTML has capabilities of form development and can include diverse sorts of input including text, checkboxes and radio buttons for gathering information from the user.
Multimedia Support: HTML provide its users with <img> so as to integrate images into the document and <audio> or <video> into the document as well.
Links: Navigation between web page and resource is done with the help of anchor points or hyperlinks created with the HTML <a> tag.
Tables: HTML allows what we can call table format tags such as <table>, <tr>, <td>, and <th>.
Responsive Design: Even though HTML alone is not capable of handling responsive behavior, when combined jointly with CSS and JavaScript, it forms the solution.
Browser Compatibility: HTML benefits from 100% support by web browsers since it enhances the availability of the content on different platforms.
Accessibility Features: HTML also supports other attributes like alt for images, ARIA roles for better accessibility to users with disabilities.
Meta Tags: Meta tags for SEO, character set, viewport settings, and other options, can be inserted into <head> section.
These features make HTML a fundamental technology for web development to design and build interactive web-age structures.
Wrap-up!
It’s crucial to understand that there is no possible way that a web developer can survive or function without fully comprehending how the DOM functions on the internet mantle. The questions defined above helps in understanding how DOM is traversed and the right way to manipulate/interact with documents. It also assist you with your interviews by familiarizing you with these concepts besides development skills amplifying.
From the interview perspective, you learn that HTML, and the Document Object Model (DOM) are very central in web development. HTML can actually be seen as the basic building blocks of actual websites, while the DOM allows for changes to HTML be made through programming languages such as JavaScript. Both concepts are crucial when it comes to design of effective and easily usable web applications. Candidates apply HTML elements, attributes, and practices and DOM manipulation to support cumputer functionality. In summary it is essential that anyone who wants to master front-end development pays special attention to the following topics.
To the best of our abilities you are trained to get through your interview at Softronix IT training Institute. From taking notes all the way to interviews, we assist with that right there. Wishing you the best for the interviews going around you, have the best coding session in advance. Connect now!
0 comments