What is the primary use of the for...in loop in JavaScript?

  • Iterating over the values of an array
  • Iterating over the properties of an object
  • Executing a block of code repeatedly
  • Iterating over elements of an array in order
The for...in loop is primarily used for iterating over the properties of an object, not for arrays. It helps access each property name (key) of an object. Attempting to use it with arrays can lead to unexpected results, as it may also iterate over non-index properties added to the array.

How can one implement a switch statement to handle multiple data types efficiently?

  • By using the "case" keyword for each data type and applying type conversion in each case.
  • By using the "default" keyword to handle unexpected data types.
  • By wrapping the switch statement in a try-catch block for error handling.
  • By using an array of functions, where each function handles a specific data type.
To handle multiple data types efficiently in a switch statement, you can create an array of functions, where each function corresponds to a specific data type. When you receive input, you can then call the appropriate function based on the data type, which offers more flexibility and avoids type conversion complexities.

You've encountered a bug in your JavaScript code where a variable is not retaining an expected value within a nested function. What feature of JavaScript should you explore to troubleshoot this issue?

  • Lexical Scoping
  • Hoisting
  • IIFE (Immediately Invoked Function Expression)
  • Event Delegation
To troubleshoot the issue of a variable not retaining an expected value within a nested function, you should explore the concept of lexical scoping. Lexical scoping (also known as static scoping) means that the scope of a variable is determined by its location within the source code, and nested functions have access to variables from their containing (parent) functions. This understanding will help you identify and fix the problem.

In a performance-critical application, minimizing the reshuffling of array elements is vital. What method might be avoided when removing elements due to its time complexity?

  • splice()
  • push()
  • pop()
  • shift()
The splice() method should be avoided when removing elements from an array in a performance-critical application because it has a time complexity of O(n) due to the need to shift elements after the removal. Methods like pop() (O(1)), shift() (O(1)), or slice() (O(n)) may be more appropriate.

In a while loop, forgetting to update the condition can lead to a/an ________ loop.

  • Infinite
  • Endless
  • Eternal
  • Unstoppable
In a while loop, if you forget to update the condition, it can lead to an "infinite" loop, where the loop continues to execute indefinitely. This can cause the program to hang or become unresponsive. It's important to ensure that the loop's condition is updated to eventually become false.

Which keyword is used to stop the loop prematurely?

  • break
  • continue
  • exit
  • return
The keyword used to stop a loop prematurely in JavaScript is "break." When "break" is encountered within a loop, it immediately exits the loop, even if the loop condition is still true or there are more iterations remaining. This is useful for early termination of a loop based on a specific condition. "continue" skips the current iteration and moves to the next one, while "exit" and "return" have different purposes and are not used for loop control.

During a job interview, you're asked about the evolution of JavaScript. The interviewer specifically wants to know about a major shift in JavaScript's usage from merely adding interactivity to web pages to being used in server-side programming. What technology or platform brought about this shift?

  • Node.js
  • Apache Tomcat
  • PHP
  • Ruby on Rails
JavaScript's major shift into server-side programming was largely enabled by Node.js. Node.js is a runtime environment that allows JavaScript to be executed on the server, making it suitable for building scalable, server-side applications. It revolutionized web development by unifying front-end and back-end languages.

Why might for...of loops be preferred when working with asynchronous code?

  • They can be used with any iterable object.
  • They automatically handle Promise resolution.
  • They are faster than traditional for loops.
  • They provide better error handling mechanisms.
For...of loops are preferred when working with asynchronous code because they automatically handle Promise resolution. When you iterate over an iterable that contains Promises, for...of will await each Promise and provide the resolved value, making it more convenient for working with asynchronous operations.

What is the primary difference between while and do-while loops in JavaScript?

  • The while loop always executes the code block at least once
  • The do-while loop is more efficient
  • The while loop is not suitable for iterating over arrays
  • The do-while loop doesn't have a condition
The primary difference is that in a while loop, the condition is checked before executing the code block. If the condition is initially false, the code block may never run. In contrast, the do-while loop guarantees that the code block is executed at least once because it checks the condition after executing the block. This makes do-while useful when you want the code to run once before checking the condition.

The ________ operator can be used to compare both value and type in JavaScript.

  • Equality (===)
  • Assignment (=)
  • Identity (==)
  • Inequality (!=)
The Equality (===) operator can be used to compare both value and type in JavaScript. It checks if two values are strictly equal, meaning they have the same value and the same data type. The other options, such as Assignment (=) and Identity (==), do not perform strict value and type comparison. Inequality (!=) checks for inequality.