Frontend Developer Interview Questions

Keep in mind that many of these questions are open ended and could lead to interesting discussions that tell you more about the person's capabilities than a straight answer would.

General Questions:

• Are you on Twitter?
  • If so, who do you follow on Twitter?
• Are you on GitHub?
  • If so, what are some examples of repos you follow
• What blogs do you follow?
• What version control systems have you used (Git, SVN etc.)?
• What is your preferred development environment? (OS, Editor, Browsers, Tools etc.)
• Can you describe your workflow when you create a web page?
• Can you describe the difference between progressive enhancement and graceful degradation?
  • Bonus points for describing feature detection
• Explain what "Semantic HTML" means.
• What browser do you primarily develop in and what developer tools do you use?
• How would you optimize a websites assets/resources?
  • Looking for a number of solutions which can include:
    • File concatenation
    • File minification
    • CDN Hosted
    • Caching
    • etc.
• Why is it better to serve site assets from multiple domains?
  • How many resources will a browser download from a given domain at a time?
• Name 3 ways to decrease page load. (perceived or actual load time)
• If you jumped on a project and they used tabs and you used spaces, what would you do?
  • Suggest the project utilize something like EditorConfig (http://editorconfig.org)
  • Conform to the conventions (stay consistant)
  • issue :retab! command
• Write a simple slideshow page
  • Bonus points if it does not use JS.
• What tools do you use to test your code's performance?
  • JSPerf (http://jsperf.com/)
  • Dromaeo (http://dromaeo.com/)
  • etc.
• If you could master one technology this year, what would it be?
• Explain the importance of standards and standards bodies.
• What is FOUC? How do you avoid FOUC?

HTML-Specific Questions:

• What's a doctype do, and how many can you name?
• What's the difference between standards mode and quirks mode?
• What are the limitations when serving XHTML pages?
  • Are there any problems with serving pages as application/xhtml+xml?
• 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?
• Can you use XHTML syntax in HTML5?
• How do you use XML in HTML5?
• What are data- attributes good for?
• What are the content models in HTML4 and are they different in HTML5?
• Consider HTML5 as an open web platform. What are the building blocks of HTML5?
• Describe the difference between cookies, sessionStorage and localStorage.

JS-Specific Questions

• Which JavaScript libraries have you used?
• Have you ever looked at the source code of the libraries/frameworks you use?
• How is JavaScript different from Java?
• What's a hashtable?
• What are undefined and undeclared variables?
• What is a closure, and how/why would you use one?
  • Your favorite pattern used to create them? argyle (Only applicable to IIFEs)
• What's a typical use case for anonymous functions?
• Explain the "JavaScript module pattern" and when you'd use it.
  • Bonus points for mentioning clean namespacing.
  • What if your modules are namespace-less?
• How do you organize your code? (module pattern, classical inheritance?)
• What's the difference between host objects and native objects?
• Difference between:javascript function Person(){} var person = Person() var person = new Person()
• What's the difference between .call and .apply?
• explain Function.prototype.bind?
• When do you optimize your code?
• Can you explain how inheritance works in JavaScript?
• When would you use document.write()?
  • Most generated ads still utilize document.write() although its use is frowned upon
• What's the difference between feature detection, feature inference, and using the UA string
• Explain AJAX in as much detail as possible
• Explain how JSONP works (and how it's not really AJAX)
• Have you ever used JavaScript templating?
  • If so, what libraries have you used? (Mustache.js, Handlebars etc.)
• Explain "hoisting".
• Describe event bubbling.
• What's the difference between an "attribute" and a "property"?
• Why is extending built in JavaScript objects not a good idea?
• Why is extending built ins a good idea?
• Difference between document load event and document ready event?
• What is the difference between == and ===?
• Explain how you would get a query string parameter from the browser window's URL.
• Explain the same-origin policy with regards to JavaScript.
• Explain event delegation.
• Describe inheritance patterns in JavaScript.
• Make this work: javascript [1,2,3,4,5].duplicator(); // [1,2,3,4,5,1,2,3,4,5]
• Describe a strategy for memoization (avoiding calculation repetition) in JavaScript.
• Why is it called a Ternary statement, what does the word "Ternary" indicate?
• What is the arity of a function?
• What is "use strict";? what are the advantages and disadvantages to using it?

JS-Code Examples:

~~3.14

Question: What value is returned from the above statement? Answer: 3

"i'm a lasagna hog".split("").reverse().join("");

Question: What value is returned from the above statement? Answer: "goh angasal a m'i"

( window.foo || ( window.foo = "bar" ) );

Question: What is the value of window.foo? Answer: "bar" only if window.foo was falsey otherwise it will retain its value.

var foo = "Hello"; (function() { var bar = " World"; alert(foo + bar); })(); alert(foo + bar);

Question: What is the outcome of the two alerts above? Answer: "Hello World" & ReferenceError: bar is not defined

var foo = [];
foo.push(1);
foo.push(2);

Question: What is the value of foo.length? **Answer: 2

var foo = {};
foo.bar = 'hello';

Question: What is the value of foo.length? **Answer: undefined

foo = foo||bar

Question: What is the mean for? **Answer: if(!foo) foo = bar

foo>>1

Question: What is the mean for? **Answer: Math.floor(foo/2)

foo|0
foo+.5|0

Question: What is the mean for? **Answer: parseInt(foo) & Math.round(foo)

function foo(bar1, bar2, bar3){}

Question: How to get the numbers of parameters? **Answer: foo.length //this example is 3

jQuery-Specific Questions:

• Explain "chaining".
• Explain "deferreds".
• What are some jQuery specific optimizations you can implement?
• What does .end() do?
• How, and why, would you namespace a bound event handler?
• Name 4 different values you can pass to the jQuery method.
  • Selector (string), HTML (string), Callback (function), HTMLElement, object, array, element array, jQuery Object etc.
• What is the effects (or fx) queue?
• What is the difference between .get(), [], and .eq()?
• What is the difference between .bind(), .live(), and .delegate()?
• What is the difference between $ and $.fn? Or just what is $.fn.
• Optimize this selector: javascript $(".foo div#bar:eq(0)")
• Difference between 'delegate()' and 'live()'?

CSS-Specific Questions:

• Describe what a "reset" CSS file does and how it's useful.
• Describe Floats and how they work.
• What are the various clearing techniques and which is appropriate for what context?
• Explain CSS sprites, and how you would implement them on a page or site.
• What are your favourite image replacement techniques and which do you use when?
• CSS property hacks, conditionally included .css files, or... something else?
• 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?
• Any familiarity with styling SVG?
• How do you optimize your webpages for print?
• What are some of the "gotchas" for writing efficient CSS?
• Do you use CSS preprocessors? (SASS, Compass, Stylus, LESS)
  • If so, 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?
  • Webfonts (font services like: Google Webfonts, Typekit etc.)
• Explain how a browser determines what elements match a CSS selector?

Optional fun Questions:

• What's the coolest thing you've ever coded, what are you most proud of?
• Do you know the HTML5 gang sign?
• Are you now, or have you ever been, on a boat.
• What are your favorite parts about the developer tools you use?
• Do you have any pet projects? What kind?
• Explain the significance of "cornify".
• On a piece of paper, write down the letters A B C D E vertically. Now put these in descending order without writing one line of code.
  • Wait and see if they turn the paper upside down
• Pirate or Ninja?
  • Bonus if it's a combo and a good reason was given (+2 for zombie monkey pirate ninjas)
• If not Web Development, what would you be doing?
• Where in the world is Carmen Sandiego?
  • Hint: their answer is always wrong
• What's your favorite feature of Internet Explorer?
• Complete this sentence: Brendan Eich and Doug Crockford are the __________ of javascript.
• jQuery: a great library or the greatest library? Discuss.
• http://www.w3schools.com/ or http://w3fools.com/