Front End Developer Interview Questions

HTML Interview Questions:

  • What does a doctype do?
  • How do you serve a page with content in multiple languages?
  • What kind of things must you be wary of when design or developing for multilingual sites?
  • What are data- attributes good for?
  • Consider HTML5 as an open web platform. What are the building blocks of HTML5?
  • Describe the difference between a cookiesessionStorage and localStorage.
  • Describe the difference between 

CSS Interview Questions:

  • What is CSS selector specificity and how does it work?
  • What’s the difference between “resetting” and “normalizing” CSS? Which would you choose, and why?
  • Describe Floats and how they work.
  • Describe z-index and how stacking context is formed.
  • Describe BFC (Block Formatting Context) and how it works.
  • What are the various clearing techniques and which is appropriate for what context?
  • How would you approach fixing browser-specific styling issues?
  • How do you serve your pages for feature-constrained browsers?
    • What techniques/processes do you use?
  • What are the different ways to visually hide content (and make it available only for screen readers)?
  • Have you ever used a grid system, and if so, what do you prefer?
  • Have you used or implemented media queries or mobile specific layouts/CSS?
  • Are you familiar with styling SVG?
  • Can you give an example of an @media property other than screen?
  • What are some of the “gotchas” for writing efficient CSS?
  • What are the advantages/disadvantages of using CSS preprocessors?
    • Describe what you like and dislike about the CSS preprocessors you have used.
  • How would you implement a web design comp that uses non-standard fonts?
  • Explain how a browser determines what elements match a CSS selector.
  • Describe pseudo-elements and discuss what they are used for.
  • Explain your understanding of the box model and how you would tell the browser in CSS to render your layout in different box models.
  • What does * { box-sizing: border-box; } do? What are its advantages?
  • What is the CSS display property and can you give a few examples of its use?
  • What’s the difference between inline and inline-block?
  • What’s the difference between the “nth-of-type()” and “nth-child()” selectors?
  • What’s the difference between a relative, fixed, absolute and statically positioned element?
  • What existing CSS frameworks have you used locally, or in production? How would you change/improve them?
  • Have you played around with the new CSS Flexbox or Grid specs?
  • Can you explain the difference between coding a web site to be responsive versus using a mobile-first strategy?
  • Have you ever worked with retina graphics? If so, when and what techniques did you use?
  • Is there any reason you’d want to use translate() instead of absolute positioning, or vice-versa? And why?

JS Interview Questions:

  • Explain event delegation.
  • Explain how this works in JavaScript.
    • Can you give an example of one of the ways that working with this has changed in ES6?
  • Explain how prototypal inheritance works.
  • What’s the difference between a variable that is: nullundefined or undeclared?
    • How would you go about checking for any of these states?
  • What is a closure, and how/why would you use one?
  • What language constructions do you use for iterating over object properties and array items?
  • Can you describe the main difference between a forEach loop and a .map() loop and why you would pick one versus the other?
  • What’s a typical use case for anonymous functions?
  • What’s the difference between host objects and native objects?
  • Explain the difference between: function Person(){}var person = Person(), and var person = new Person()?
  • Explain the differences on the usage of foo between function foo() {} and var foo = function() {}
  • Can you explain what .call and .apply do? What’s the notable difference between the two?
  • Explain Function.prototype.bind.
  • What’s the difference between feature detection, feature inference, and using the UA string?
  • Explain “hoisting”.
  • Describe event bubbling.
  • Describe event capturing.
  • What’s the difference between an “attribute” and a “property”?
  • What are the pros and cons of extending built-in JavaScript objects?
  • What is the difference between == and ===?
  • Explain the same-origin policy with regards to JavaScript.
  • Why is it called a Ternary operator, what does the word “Ternary” indicate?
  • What is strict mode? What are some of the advantages/disadvantages of using it?
  • What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript?
  • What tools and techniques do you use debugging JavaScript code?
  • Explain the difference between mutable and immutable objects.
    • What is an example of an immutable object in JavaScript?
    • What are the pros and cons of immutability?
    • How can you achieve immutability in your own code?
  • Explain the difference between synchronous and asynchronous functions.
  • What is event loop?
    • What is the difference between call stack and task queue?
  • What are the differences between variables created using letvar or const?
  • What are the differences between ES6 class and ES5 function constructors?
  • Can you offer a use case for the new arrow => function syntax? How does this new syntax differ from other functions?
  • What advantage is there for using the arrow syntax for a method in a constructor?
  • What is the definition of a higher-order function?
  • Can you give an example for destructuring an object or an array?
  • Can you give an example of generating a string with ES6 Template Literals?
  • Can you give an example of a curry function and why this syntax offers an advantage?
  • What are the benefits of using spread syntax and how is it different from rest syntax?
  • How can you share code between files?
  • Why you might want to create static class members?

Network Questions

  • Traditionally, why has it been better to serve site assets from multiple domains?
  • Do your best to describe the process from the time you type in a website’s URL to it finishing loading on your screen.
  • What are the differences between Long-Polling, Websockets and Server-Sent Events?
  • Explain the following request and response headers:
    • Diff. between Expires, Date, Age and If-Modified-…
    • Do Not Track
    • Cache-Control
    • Transfer-Encoding
    • ETag
    • X-Frame-Options
  • What are HTTP methods? List all HTTP methods that you know, and explain them.
  • What is domain pre-fetching and how does it help with performance?

Testing Questions

  • What are some advantages/disadvantages to testing your code?
  • What tools would you use to test your code’s functionality?
  • What is the difference between a unit test and a functional/integration test?
  • What is the purpose of a code style linting tool?