What is the difference between let and const in JavaScript?
What is a callback function in JavaScript?
What is the difference between “null” and “undefined” values in JavaScript?
What is event bubbling in JavaScript?
What is a closure function in JavaScript?
What is the difference between “call” and “apply” methods in JavaScript?
What is a promise in JavaScript?
What is the difference between a synchronous and asynchronous JavaScript code execution?
What is the difference between the “let” and “var” keywords?
What are some of the common design patterns used in JavaScript, and why are they useful?
What is the difference between a for loop and a forEach loop in JavaScript?

10 JavaScript Interview Questions

What is the difference between let and const in JavaScript?

Response: Both let and const are used for declaring variables, but let variables can be reassigned a new value, while const variables cannot be reassigned a new value.

Explanation: This question tests the candidate’s understanding of variable declaration in JavaScript. A good response should explain the differences between let and const and provide examples of when each keyword should be used.

What is a callback function in JavaScript?

Response: A callback function is a function that is passed as an argument to another function and is executed after that function has completed its operation.

Explanation: This question tests the candidate’s understanding of callback functions in JavaScript. A good response should explain what a callback function is and provide examples of how it is used in JavaScript programming.

What is the difference between “null” and “undefined” values in JavaScript?

Response: Null is a value that represents the intentional absence of any object value, while undefined is a value that represents the absence of a value or an uninitialized value.

Explanation: This question tests the candidate’s understanding of null and undefined values in JavaScript. A good response should explain the differences between these two values and provide examples of when each value should be used.

What is event bubbling in JavaScript?

Response: Event bubbling is the process by which an event propagates from the target element to its parent elements in the DOM tree.

Explanation: This question tests the candidate’s understanding of event handling in JavaScript. A good response should explain what event bubbling is and provide examples of how it works in JavaScript programming.

What is a closure function in JavaScript?

Response: A closure function is a function that has access to its outer function’s variables, even after the outer function has returned.

Explanation: This question tests the candidate’s understanding of closure functions in JavaScript. A good response should explain what a closure function is and provide examples of how it works in JavaScript programming.

What is the difference between “call” and “apply” methods in JavaScript?

Response: Both call and apply are methods used to call a function with a specified object as the this value, but call takes a comma-separated list of arguments, while apply takes an array of arguments.

Explanation: This question tests the candidate’s understanding of call and apply methods in JavaScript. A good response should explain the differences between these two methods and provide examples of when each method should be used.

What is a promise in JavaScript?

Response: A promise is an object that represents the eventual completion (or failure) of an asynchronous operation and allows handling the result asynchronously.

Explanation: This question tests the candidate’s understanding of promises in JavaScript. A good response should explain what a promise is and provide examples of how it works in JavaScript programming.

What is the difference between a synchronous and asynchronous JavaScript code execution?

Response: Synchronous code execution is the traditional way of running code where one operation has to finish before the next operation can begin. Asynchronous code execution is a newer way of running code where multiple operations can run at the same time.

Explanation: This question tests the candidate’s understanding of synchronous and asynchronous code execution in JavaScript. A good response should explain the differences between these two styles of code execution and provide examples of when each style should be used.

What is the difference between the “let” and “var” keywords?

Response: Both let and var are used for declaring variables, but let is block-scoped, while var is function-scoped.

Explanation: This question tests the candidate’s understanding of variable scoping in JavaScript. A good response should explain the differences between let and var and provide examples of when each keyword should be used.

What are some of the common design patterns used in JavaScript, and why are they useful?

Response: Some common design patterns used in JavaScript include the module pattern, the singleton pattern, and the observer pattern. These patterns are useful because they provide developers with reusable, modular code that can be easily maintained and extended.

Explanation: This question tests the candidate’s knowledge of common design patterns in JavaScript and their practical applications. A good response should provide examples of how these patterns can be used to create more efficient and maintainable code, and explain why they are useful for JavaScript developers.

What is the difference between a for loop and a forEach loop in JavaScript?

Response: A for loop is a traditional loop that uses a counter variable to iterate over a collection of values. A forEach loop is a higher-order function that iterates over an array and executes a callback function for each element.

Explanation: This question tests the candidate’s understanding of loop constructs in JavaScript. A good response should explain the differences between for and forEach loops and provide examples of when each loop should be used.