Closures can help in creating data _________ by providing data privacy and are used to create factory functions for building similar objects.

  • Encapsulation
  • Abstraction
  • Inheritance
  • Isolation
Closures provide a form of data isolation, which is essential for data privacy in JavaScript. They allow you to encapsulate data within a function's scope, making it inaccessible from the outside, thus achieving data isolation and privacy. This concept is often used in creating factory functions.

You're working on a project where you have to fetch data from an API and display it on a webpage without refreshing it. Which technology would be most suitable for this?

  • WebSockets
  • Fetch API
  • REST API
  • GraphQL
The Fetch API is commonly used for making asynchronous network requests, including fetching data from APIs and updating web pages without refreshing. While WebSockets are used for real-time communication, REST and GraphQL are architectural approaches, not technologies.

How do arrow functions affect the call stack and debugging in JavaScript?

  • They have no impact on the call stack.
  • They add an extra layer to the call stack.
  • They make debugging more straightforward.
  • They can cause stack overflow errors.
Arrow functions have no impact on the call stack, as they do not create their own execution context or call themselves recursively. This means they don't contribute to the call stack depth, making it easier to avoid stack overflow errors in certain cases. However, it's essential to understand how this behavior can affect debugging and performance when using arrow functions in JavaScript.

You are troubleshooting an issue where the Fetch API call to a third-party API is not returning any data, and you suspect it might be due to a CORS policy. How might you validate and debug this issue?

  • Use a CORS proxy
  • Check the browser console
  • Modify the server's CORS policy
  • Reboot the server
To validate and debug a CORS (Cross-Origin Resource Sharing) issue, you can check the browser console for error messages, which often provide information about the CORS policy violation. Modifying the server's CORS policy or using a CORS proxy can help resolve such issues. Rebooting the server is unlikely to fix CORS problems.

What will be the output of console.log(typeof null); in JavaScript?

  • "object"
  • "null"
  • "undefined"
  • "number"
The expression console.log(typeof null); in JavaScript will output "object." This is a quirk in JavaScript because typeof null returns "object," even though null is not an object but a special value representing the absence of a value.

In which scenario might you prefer to use Object.create(null) over {} to create an empty object?

  • When you need an empty object with no prototype chain (no inherited properties or methods)
  • When you need an empty object with default prototype properties
  • When you need an object with prototype properties
  • When you need an object with getter and setter methods
Object.create(null) is used when you want an empty object with no prototype chain. This is useful when you want to create a clean slate object without inheriting any properties or methods from the Object prototype.

The insertBefore method is used to insert an element before the _________ child of a specified parent.

  • first
  • last
  • next
  • previous
The insertBefore method is used to insert an element before the specified next child of a parent element. It allows you to precisely control the position of the new element within the parent's children.

How do you select the last child of an element using pure JavaScript?

  • lastChild
  • element.lastChild
  • lastElementChild
  • element.lastElementChild
To select the last child of an element using pure JavaScript, you should use the lastElementChild property of the element. This property returns the last element among the child elements of the specified parent element. The other options, lastChild, element.lastChild, and lastElementChild, do not provide the same functionality.

You are reading through a codebase and find that a block of code within an "else if" statement is not being executed, despite it seeming like the condition should be true. What are some steps you could take to troubleshoot this issue?

  • Check condition logic
  • Verify variable values
  • Examine code dependencies
  • Debug with console statements
Troubleshooting such issues involves checking the condition logic within the "else if" statement. Verify that the condition is correctly formulated and that the variables being compared have the expected values. Additionally, inspecting code dependencies and using console statements for debugging can help identify the problem.

You’re developing a web application and need to add a feature where a modal appears when a button is clicked, but users complain that the page scrolls up every time they click the button. What JavaScript method could you use to prevent this default behavior?

  • event.stopPropagation()
  • event.preventDefault()
  • event.stopImmediatePropagation()
  • event.cancelBubble()
To prevent the default behavior of a button click, you can use the event.preventDefault() method. This method stops the browser from executing the default action associated with the event, such as submitting a form or navigating to a new page, in this case, preventing the page from scrolling up. event.stopPropagation() is used to stop the event from bubbling up the DOM tree but won't prevent the default behavior.