Vani Ananthuni


Front End Developer/Engineer Interview Questions

These are the questions that I was either asked in the interviews or I have asked myself while learning. 

//over 100 questions


  1. How do you define “semantic” markup? 
  2. How do you Optimizing your pages for speculative parsing?
  3. What are the new features in html5?
  4. When and why would you use div?
  5. Difference between <aside> and <article>
  6. What is !DOCTYPE? What happens if you do not include it in an HTML file?
  7. How to block the click event of a <a> with out using event blocker?  ( add an onclick function that returns false to <a> )
  8. List some tags which do not need closing tags. //<img> <br> <hr> <p>
  9.  What are some common lists that are used when designing a page? //Ordered, Unordered, Menu, Dictionary, Definition
  10. What are replacements for <b> and <italic> in semantic HTML? //<strong> and <em>
  11. How is the color of a bullet determined?
  12. What are Canvas and SVG in HTML5?
  13. Which video formats are supported by HTML5? //mp4, webm, ogg
  14. How to implement autocomplete feature in HTML5? // <datalist>
  15. What are the new input types used for validation in HTML5?
  16. What's the difference between standards mode and quirks mode?
  17. How do you serve a page with content in multiple languages?
  18. Describe the difference between <script>, <script async> and <script defer>.
  19. What is progressive rendering?


  1. What are the new features in CSS3?
  2. How would you integrate multiple CSS files?
  3. What's the difference between a relative, fixed, absolute and statically positioned element?
  4. How would you reduce the size of CSS file(s)? answer
  5. What are preprocessors and why are they used? List advantages and disadvantages.
  6. What is the difference between inline and block styling?
  7. What is specificity in CSS? (answer)
  8. What is the use of * selector? How often should you use it?
  9. What is CSS Reset? What are the issues with using it?
  10. What are Bootstrap and Foundation? What preprocessors are written in?
  11. What are the differences between class and id in css?
  12. How to clear floats? (answer)
  13. What is the difference between inline, embedded and external style sheets?
  14. What are the benefits of CSS sprites?
  15. What is CSS Box model?
  16. How is responsive design different from adaptive design?
  17. Describe pseudo-elements and discuss what they are used for.
  18. What is the purpose of the z-index and how is it used?
  19. Explain the difference between visibility: hidden and display: none?
  20. What is tweening? How to achieve it in CSS? //matrix, translate, rotate, scale etc.
  21. What is RWD? What are the different ways to achieve it? //bootstrap, media queries, fluid grids, flexible images
  22. What's the difference between "resetting" and "normalizing" CSS? Which would you choose, and why?
  23. Create a shining transparent effect over an image. //filter opacity + gradient.


  1. What are the new features of ES6/EcmaScript2015? (answer) (click here for PDF Format of everything)
  2. What is BOM? //Browser Object Model
  3. What is the difference between function() and Function()?
  4. What is the difference between innerHTML and appendChild()?
  5. Is JavaScript case sensitive language? (Yes)
  6. What are the different ways to create an object? (answer)
  7. What does Object.assign do? (answer)
  8. What are polyfills?
  9. What is dependency injection?
  10. What are singletons?
  11. Explain event delegation
  12. What are the different pop up boxes available in javascript? // Alert, Confirm, Prompt
  13. What are a few reserved words in JS? What are valid  variable names? (answer)
  14. Write a function that returns the largest number is an array of arrays. 
  15. Write a function that returns the of the number with highest frequency.
  16. What's the difference between host objects and native objects?
  17. How do you organize your code? (module pattern, classical inheritance?)
  18. Write a function that returns the frequency of all the values in an object.
  19. Explain how this works in JavaScript.
  20. What is defer in JavaScript?
  21. Difference between document load event and document ready event?
  22. What is "use strict";? what are the advantages and disadvantages to using it?
  23. Difference between: function Person(){}, var person = Person(), and var person = new Person()?
  24. Write a function that returns the sum of all the even numbers and the sum of all odd numbers.
  25. Write a function that returns Fibonacci sequence and nth element in the series.  
  26. What are MV* and MVC? What are your opinions on Angular, React, Ember, Backbone?
  27. Explain the following concepts in Javascript: Closures, Prototypes, Currying.
  28. What is <noscript> tag and why is it used?
  29. What is the difference between == and === ?
  30. What is the difference between undeclared, undefined and null? 
  31. What is the typeof null? //number
  32. How to identify all the images on a page, including backgrounds? //$(*’).filter(function(){return $(this).css(‘background-image'=)});
  33. What are the pros and cons of using Promises instead of callbacks?
  34. Is JS strictly typed of strongly typed language?
  35. What is the typeof console and console.log? // object & function
  36. What are the rendering problems with browsers < IE8?
  37. What's a typical use case for anonymous functions?
  38. What are the differences between frameworks and library?
  39. Write a function that returns all the prime numbers less than the argument. 
  40. Write a function to check if two strings are anagrams of each other.
  41. Write a function that checks if the given number is a valid US phone number.
  42. What are the differences between call() and apply()? Explain bind().
  43. Write a function that returns the longest palindrome in a string and test it.
  44. Write a function that takes two arrays and returns one sorted array. (array should be sorted while creating)
  45. Count the number of words in a string without using split(“)
  46. Write a javascript code for carousel widget.
  47. What's a typical use case for anonymous functions?
  48. Explain "hoisting".
  49. What's the difference between an "attribute" and a "property"?
  50. How can you change style to one particular browser?
  51. Explain block scoping in Javascript. (JS does not support block scoping)
  52. if(‘false’){alert(“true”);} What is the output of this code? //true
  53. What are falsy values?
  54. What is your opinion on Object Oriented Javascript?
  55. What type of inheritance is used in javascript? //prototype
  56. What is “class” keyword used for? (answer)
  57. What is the difference between classical inheritance and prototypal inheritance?
  58. What are two-way data binding and one-way data flow, and how are they different?
  59. What are the pros and cons of monolithic vs microservice architectures?
  60. What is asynchronous programming, and why is it important in JavaScript?
  61. What are the your most and least favorite parts of JS?

Web Technologies

  1. What is the difference between http and https? 
  2. How would you implement session management? Explain cookies and caching.
  3. What happens when you type a URL in the browser and press enter? Describe the role of cache in this case.
  4. How would you improve the performance of a website if the client likes the UI but feels like its slow?
  5. How do you test the website in different browsers?
  6. How to implement Google like autocomplete feature?
  7. Explain the difference between event bubbling and event capture.
  8. What are the difference rendering problems you have had with different browsers?
  9. How would you update a live websites styling if it’s cached?
  10. Explain latency. (answer
  11. How would you troubleshoot a blank page when you publish the website through local server.
  12. What is the difference between regular web applications and single page web applications?
  13. How to create single page web applications without using any frameworks.
  14. Explain what ARIA and screenreaders are, and how to make a website accessible.
  15. Describe the difference between a cookie, sessionStorage and localStorage.
  16. What are some ways you may improve your website's scrolling performance?
  17. Explain the difference between layout, painting and compositing.
  18. What update of the upcoming web standards excite you? w3standards
  19. How do you like your coffee? 


  1. What is javascript’s window object equivalent in node.js? //global
  2. What is a callback hell? How to avoid it?


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