20 JavaScript DOM Interview Questions and Answers

The Document Object Model (DOM) is a platform- and language-neutral interface that will be used to process and manipulate structured documents. When you are interviewing for a position that will require you to work with the DOM, it is important to be prepared to answer questions about your experience and knowledge. This article discusses some of the most common JavaScript DOM interview questions and provides tips on how to answer them.

JavaScript DOM Interview Questions and Answers

Here are 20 commonly asked JavaScript DOM interview questions and answers to prepare you for your interview:

1. What is the DOM?

The DOM is the Document Object Model, which is a tree-like structure that represents the HTML document. It is used by JavaScript to access and manipulate the document.

2. Can you explain what an event listener is in JavaScript?

An event listener is a function that is automatically called when a specified event occurs. For example, if you have a button on a web page, you can use an event listener to automatically call a function when the button is clicked.

3. How can you change styles of a particular element using JavaScript?

You can change styles of a particular element using JavaScript by accessing the element’s style property. This property is an object that contains all of the element’s style information. To change a specific style, you would simply set the appropriate property of the style object to the new value. For example, if you wanted to change the color of an element, you would do the following:

element.style.color = “new color”;

4. Can you name some important events provided by JavaScript? Which ones do you use frequently and why?

There are a number of important events provided by JavaScript, and which ones you use frequently will depend on your particular needs. Some of the more commonly used events include “onload”, which is triggered when a page or element is loaded, and “onclick”, which is triggered when an element is clicked on. Other important events include “onmouseover”, “onmouseout”, and “onkeypress”. Each of these events can be used to trigger a specific action, such as loading a new page or displaying an alert message.

5. Can you explain how to create custom HTML attributes, then get their values?

You can create custom HTML attributes by using the setAttribute() method. Once you have created a custom attribute, you can then get its value by using the getAttribute() method.

6. Is it possible to remove all child nodes from a node object? If yes, then how?

Yes, it is possible to remove all child nodes from a node object. This can be done by setting the node’s innerHTML property to an empty string.

7. When would you use the querySelectorAll() method in JavaScript?

The querySelectorAll() method is used when you want to select all elements that match a given CSS selector. This is useful when you want to apply a style to all elements that match a certain selector, or when you want to perform some other action on all elements that match a certain selector.

8. How can we enable or disable form elements using JavaScript?

You can use the disabled property to enable or disable form elements using JavaScript. This property can be set to true or false, depending on whether you want to enable or disable the element. For example, to disable a form element, you would set the disabled property to true.

9. How can we toggle between hiding and showing content using JavaScript?

There are a few different ways to toggle between hiding and showing content using JavaScript. One way would be to use the CSS style property “display” and set it to “none” to hide the content, and then set it back to “block” to show it again. Another way would be to use the “visibility” style property and set it to “hidden” to hide the content, and then set it back to “visible” to show it again.

10. What are namespace objects in JavaScript?

Namespace objects are used to group together related objects, properties, and methods. In JavaScript, the default namespace is the global object. However, you can create your own namespace objects to keep your code organized. For example, you might create a namespace object for all of the objects related to a particular website or application.

11. What are the different types of errors that can occur while writing JavaScript code?

The different types of errors that can occur while writing JavaScript code include syntax errors, runtime errors, and logic errors. Syntax errors occur when the code is not valid according to the JavaScript syntax. Runtime errors occur when the code tries to execute an invalid operation. Logic errors occur when the code does not produce the expected results.

12. Can you explain how to access local variables in one window/frame from another if they’re not part of any document category?

You can access local variables in another window or frame by using the window.name property. This property returns a string that represents the name of the window. You can then use this string to access the local variables in the other window or frame.

13. Can you explain how to detect browser type and version using JavaScript?

You can detect browser type and version using the navigator object in JavaScript. This object contains information about the browser, including the name and version. You can use this object to detect whether the browser is Internet Explorer, Firefox, Safari, etc. and to determine the version number.

14. What’s the difference between closing a window with the close() and self.close() methods?

The close() method will close the current window, while the self.close() method will close the current frame or window.

15. How does variable hoisting work in JavaScript?

Variable hoisting is a process in JavaScript whereby variables and function declarations are moved to the top of their respective scope before code execution. This can lead to some unexpected results if you are not aware of how hoisting works. For example, if you have a variable that is declared at the bottom of a function, it will still be accessible at the top of the function.

16. What is a promise in JavaScript?

A promise is an object that represents the eventual completion or failure of an asynchronous operation. In other words, it is a placeholder for a future value. Promises are used in many places in JavaScript, including the fetch() API, and they provide a way to handle asynchronous operations in a more synchronous fashion.

17. What is a callback function?

A callback function is a function that is passed as an argument to another function. The callback function is then invoked inside of the other function. Callback functions are often used to perform asynchronous tasks.

18. What are anonymous functions in JavaScript?

Anonymous functions are functions that are not given a name. They are often used as callback functions, or functions that are passed into another function as an argument.

19. Can you explain what this refers to in JavaScript?

The Document Object Model, or DOM, is a way of representing HTML documents as a tree structure. This makes it easy to access and manipulate the elements of a page with JavaScript.

20. What is the importance of null prototypes in JavaScript?

The null prototype is important in JavaScript because it provides a way to create an object that doesn’t inherit any properties from its prototype. This can be useful when you want to create an object that doesn’t have any of the built-in properties or methods of other objects, and can help to prevent unexpected behavior.