JavaScript DOM: Questions for TechPrep

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1. What is the Document Object Model (DOM)?

Answer: The Document Object Model (DOM) is a programming interface for web documents that provides a structured representation of the HTML or XML document. It allows programs to dynamically access, update, and modify the content, structure, and style of a web page.

2. What is a node in the DOM?

Answer: In the DOM, a node is an interface representing an object in the document tree. It can be an element, attribute, text, comment, or the document itself. Nodes are organized in a hierarchical structure, with the document node at the top.

3. What are the different types of nodes in the DOM?

Answer: The DOM defines several types of nodes: element nodes represent HTML elements, text nodes contain text within elements, comment nodes represent comment text, document nodes represent the entire document, and attribute nodes hold attribute values.

4. What is the difference between the innerHTML and outerHTML properties?

Answer: The innerHTML property represents the HTML content of an element, including any child elements, whereas the outerHTML property represents the HTML content of an element along with the element itself as a string.

5. How do you create a new element with JavaScript?

Answer: To create a new element in the DOM, you can use the createElement() method provided by the document object. You specify the element type as an argument, like document.createElement('div'), and it returns a new element node.

6. How do you add an element to the DOM?

Answer: To add an element to the DOM, you can use the appendChild() or insertBefore() methods. The appendChild() method adds a new child element at the end of the specified parent element, while insertBefore() inserts a new child element before an existing child element.

7. What is the parentNode property?

Answer: The parentNode property returns the parent node of an element. It provides a way to traverse up the DOM tree from a specific node to its parent node.

8. How do you remove an element from the DOM?

Answer: To remove an element from the DOM, you can use the removeChild() method. It requires selecting the parent node of the element and calling removeChild() on that parent node, passing the element to be removed as an argument.

9. How do you select an element in the DOM?

Answer: There are various ways to select an element in the DOM. The querySelector() method allows you to select an element using CSS-style selectors, while the getElementById() method selects an element based on its unique ID attribute.

10. What is event bubbling in the DOM?

Answer: Event bubbling is a mechanism in the DOM where an event triggered on a particular element will first be handled by that element's own event listeners, then propagated up through its parent elements, allowing their event listeners to handle the event as well.

11. How do you stop event propagation in the DOM?

Answer: To stop event propagation and prevent further event listeners from being invoked, you can use the stopPropagation() method on the event object. By calling event.stopPropagation(), you can prevent the event from bubbling up the DOM tree.

12. What is event capturing in the DOM?

Answer: Event capturing is the reverse process of event bubbling. It allows event handlers to be executed on parent elements before reaching the target element. During the capturing phase, the event starts at the top of the DOM tree and propagates down to the target element.

13. How do you capture events in the DOM?

Answer: Event capturing can be achieved by using the addEventListener() method with the third parameter set to true. For example, element.addEventListener('click', handler, true). This will invoke the event handler during the capturing phase.

14. How do you remove an event listener in the DOM?

Answer: To remove an event listener from an element, you can use the removeEventListener() method. Pass in the same event type, event handler function, and other options used when adding the listener.

15. What is the offsetTop property?

Answer: The offsetTop property returns the distance, in pixels, between the top of an element and the top of its offset parent. It helps find the vertical position of an element within its parent element.

16. What is the offsetLeft property?

Answer: The offsetLeft property returns the distance, in pixels, between the left edge of an element and the left edge of its offset parent. It helps find the horizontal position of an element within its parent element.

17. How do you get the width and height of an element in the DOM?

Answer: To retrieve the width and height of an element, you can use the offsetWidth and offsetHeight properties. These properties return the layout width and height of the element, including padding, border, and scrollbars.

18. What is the getBoundingClientRect() method?

Answer: The getBoundingClientRect() method returns a DOMRect object that describes the size and position of an element relative to the viewport. It provides values for top, left, right, bottom, width, height, and other measurements.

19. How do you check if an element has a class in the DOM?

Answer: You can check if an element has a specific class by using the classList.contains() method. By calling element.classList.contains('class-name'), you can determine if the element has the specified class.

20. How do you add a class to an element in the DOM?

Answer: To add a class to an element, use the classList.add() method. Call element.classList.add('class-name') to append the specified class name to the element's list of classes.

21. How do you remove a class from an element in the DOM?

Answer: To remove a class from an element, use the classList.remove() method. Call element.classList.remove('class-name') to remove the specified class from the element's list of classes.

22. What is the difference between attributes and properties in the DOM?

Answer: Attributes represent the initial, static values defined in HTML markup, while properties are dynamic values that can change during runtime. Attributes and properties are related, as changing a property often updates the corresponding attribute and vice versa.

23. How do you set an attribute in the DOM?

Answer: You can set an attribute on an element using the setAttribute() method. Use element.setAttribute('attribute-name', 'attribute-value') to set or modify an attribute.

24. How do you get an attribute in the DOM?

Answer: To retrieve the value of an attribute from an element, you can use the getAttribute() method. Call element.getAttribute('attribute-name') to get the value of the specified attribute.

25. How do you remove an attribute from an element in the DOM?

Answer: You can remove an attribute from an element using the removeAttribute() method. Use element.removeAttribute('attribute-name') to remove the specified attribute from the element.

26. How do you create an event in the DOM?

Answer: To create a custom event in the DOM, you can use the document.createEvent() method. This method allows you to create an event object that can be customized with specific properties and dispatched to trigger event listeners.

27. How do you dispatch an event in the DOM?

Answer: Dispatching an event in the DOM involves using the dispatchEvent() method on an element. After creating the event object, use element.dispatchEvent(eventObject) to trigger the event and execute the corresponding event listeners.

28. How do you get the position of the mouse pointer in the DOM?

Answer: To determine the position of the mouse pointer within the document, you can use the clientX and clientY properties available on the MouseEvent object. These properties indicate the coordinates relative to the viewport.

29. How do you detect if the user is scrolling in the DOM?

Answer: You can detect scrolling in the DOM by listening for the scroll event on the document or specific elements. By attaching an event listener to the scroll event, you can execute code whenever the user scrolls the page.

30. How do you detect if an element is visible in the DOM?

Answer: Determining if an element is visible in the DOM typically involves checking if its coordinates or dimensions are within the visible portion of the viewport. By using the getBoundingClientRect() method and comparing the element's position to the viewport's boundaries, you can determine if it is visible or not.