20 JavaScript Events Interview Questions and Answers

JavaScript is a versatile programming language that can be used to create a wide variety of applications and websites. When interviewing for a position that involves JavaScript, you can expect to be asked questions about events. Events are a important part of JavaScript and understanding how they work is essential for any developer. In this article, we will review some of the most common JavaScript events interview questions and provide tips on how to answer them.

JavaScript Events Interview Questions and Answers

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

1. What are JavaScript events?

JavaScript events are the mechanisms by which JavaScript code can interact with HTML elements. When an event occurs, such as a user clicking on a button, the associated JavaScript code will be executed. This allows for a dynamic and responsive user interface.

2. Can you explain the different types of events available in JavaScript?

There are a variety of events available in JavaScript, including “onclick,” “onmouseover,” and “onkeypress.” Each event is triggered by a specific user interaction and can be used to execute a specific function.

3. How is an event triggered or fired?

When an event is triggered or fired, it means that something has happened that is of interest to the event listener. The event listener is then able to take some action, such as responding to the event or executing some code.

4. How do you handle multiple events with a single function in JavaScript?

You can use event delegation to handle multiple events with a single function. This involves attaching a single event listener to a parent element, and then using event bubbling to handle the event for all child elements that match the specified selector.

5. What’s the difference between an Event Handler and an Event Listener?

An Event Handler is a function that is automatically called in response to an event. An Event Listener is an object that is notified when an event occurs. The listener can then respond to the event by calling an Event Handler.

6. What does “event bubbling” mean in JavaScript?

Event bubbling is a type of event propagation where events “bubble” up from the innermost element to the outermost element. So if you have a click event on a button inside of a div, the event will first be triggered on the button, then on the div, and then on any other parent elements.

7. What is the difference between stopPropagation and preventDefault methods?

The stopPropagation method will stop an event from bubbling up the DOM tree, while the preventDefault method will prevent the default action of an event from being triggered.

8. Can you give me some examples of HTML DOM Events?

Some examples of HTML DOM events include onload, onunload, onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, and onkeyup.

9. What is the purpose of using the onblur() method?

The onblur() method is used to specify what should happen when an element loses focus. This is often used to validate input fields before the user moves on to the next field.

10. Is it possible to use an arrow function as an event handler? If yes, then how?

Yes, it is possible to use an arrow function as an event handler. You would just need to make sure that the function is bound to the correct element. For example:

“`
document.getElementById(“myButton”).addEventListener(“click”, () => {
console.log(“Button was clicked!”);
});
“`

11. In what order are events handled in JavaScript?

Events are handled in JavaScript in the order in which they occur. This means that if two events happen at the same time, the event that happened first will be handled first.

12. Are there any limitations when handling browser-specific events like mouseover() or keypress()?

There can be some limitations when handling browser-specific events, as different browsers may interpret these events differently. For example, the mouseover event may be triggered when the mouse enters an element, moves over an element, or leaves an element, depending on the browser. It is important to test your code in different browsers to ensure that it behaves as expected.

13. Which is better, inline functions or external functions for event handlers? Why?

It is generally considered best practice to avoid inline functions for event handlers, as they can create anonymous functions that are difficult to debug. Additionally, inline functions can create closures that can lead to unexpected behavior. External functions are generally easier to debug and manage, so they are generally the preferred option.

14. How can you cancel the effect of an event once it has been triggered?

The event.preventDefault() method will cancel the default action of an event (such as a link redirecting to a new page). The event.stopPropagation() method will stop the event from bubbling up the DOM tree, preventing any parent handlers from being executed.

15. What happens if an event handler returns false?

If an event handler returns false, it will cancel the event from being processed any further. This can be used to stop a form from being submitted, for example.

16. What are synthetic events in ReactJS?

Synthetic events are React’s way of normalizing events so that they have consistent properties across different browsers. This is important because it allows React developers to write code that will work in the same way regardless of which browser is being used. Synthetic events also allow React to pool event objects and reuse them, which helps to improve performance.

17. Are there any differences in handling events from touch devices vs regular computers?

Yes, there are some differences in how events are handled on touch devices as opposed to regular computers. For example, on a touch device, you may need to account for the fact that a user may be trying to scroll the page at the same time as they are trying to interact with an element on the page. This can be done by using event delegation, which is a technique for listening for events at a higher level in the DOM tree and then propagating those events down to the specific elements that need to handle them.

18. What is the significance of using passive event listeners in JavaScript?

Passive event listeners are event listeners that do not cancel the event’s default behavior. This is significant because it allows for things like scrolling to continue even if the event listener is triggered. This can be important for performance, as cancelling the default behavior can be expensive.

19. What’s the best way to minimize problems that may arise due to poor management of event listeners?

One way to minimize problems that may arise due to poor management of event listeners is to make sure that you are using event delegation. This means that you are attaching a single event listener to a parent element, and then relying on event bubbling to take care of the rest. This can help to cut down on memory usage and can make it easier to manage your event listeners.

20. Do you think it’s necessary to remove event listeners after they’ve been executed? Why or why not?

It is not necessary to remove event listeners after they have been executed, but it is generally considered good practice. The reason for this is that if you do not remove the event listener, it will continue to execute even if the element it is attached to no longer exists. This can lead to memory leaks and other problems.