A list of questions you can use to help interview potential candidates for a front-end development position.
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@version 1.0


@bentruyman (http://bentruyman.com/), @roger_raymond (http://twitter.com/iansym), @ajpiano (http://ajpiano.com/), @paul_irish (http://paulirish.com/), @SlexAxton (http://alexsexton.com/), @boazsender (http://boazsender.com/), @miketaylr (http://miketaylr.com/), @vladikoff (http://vladfilippov.com/), @gf3 (http://gf3.ca/), @jon_neal (http://twitter.com/jon_neal), @wookiehangover (http://wookiehangover.com/) and @darcy_clarke (http://darcyclarke.me)

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?

  • What is your preferred development enviroment? (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 degredation?

    They are essentially the same thing, but you start PE by creating something that is accessible to as large an audience on a variety of devices as possible and then enhance in a way that won't break the site for users who cannot access those features properly. This process, when done correctly ensures graceful degradation, or the ability of your site/app to degrade without breaking to support those lower ability-ed browsers/users.

    • Bonus points for the answer "no one can"
    • Extra bonus points for describing feature detection
  • Explain what "Semantic HTML" means. (Taken from Wikipedia)

    "Semantic HTML is the use of HTML markup to reinforce the semantics, or meaning, of the information in webpages rather than merely to define its presentation (look). Semantic HTML is processed by regular web browsers as well as by many other user agents. CSS is used to suggest its presentation to human users.""

  • What does "minification" do?

    This can depend on the level of minification you are doing, but in general it removes comments/white space to decrease the file size. More aggressive approaches might replace long variable names with single letter variable names. This is an uglification of your code that makes it unreadable, but extremely compressed. You can also gzip it for faster file serving.

  • Why is it better to serve site assets from multiple domains?

    Concurrent downloads because a browser will only download a certin number of resources per domain at a time. This can greatly decrease page load times.

    • How many resources will a browser download from a given domain at a time?

      Depends. IE6/7 will only pull 2 assets a time from one domain. I could not find specific #s for other browsers.

  • If you have 8 different stylesheets for a given design, how would you integrate them into the site?

    File Concat

    • Looking for file concatenation.
    • Points off for @import, unless it works in conjunction with a build system.
  • If you jumped on a project and they used tabs and you used spaces, what would you do?

    • 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?

    PageSpeed/Yslow/HTML/CSS Validator

  • If you could master one technology this year, what would it be?

    Javascript testing

  • Name 3 ways to decrease page load. (perceived or actual load time)

    Concatentation,Minification,Gzip of assets. Removing/decreasing blocking scripts loading on the page as much as possible (Async tag where supported) Make sure pages are valid markup

  • Explain the importance of standards.

    Decreases different ways people can code to get the same output, at least in one browser. Decreases debugging time if code is more standardizd/familiar to you Consistency across browser rendering (If the browser is standard in its implementation of standards)

HTML-Specific Questions:

  • What's a doctype do, and how many can you name?

    Declaration of the document's type, so a validator can parse the content effective. Also, for standards so you know and code the HTML page correctly. XHTML, HTML 4.01, Loose, Transitional, Strict, HTML5 doctype

  • What's the difference between standards mode and quirks mode?

    Standards will adhere to and validate based on the doctype specificed while quirks mode may not have a doctype defined or invalid markup used which causes the browser to render the document in a fallback type of way. In computing, quirks mode refers to a technique used by some web browsers for the sake of maintaining backward compatibility with web pages designed for older browsers, instead of strictly complying with W3C and IETF standards in standards mode. - From wikipedia

  • What are the limitations when serving XHTML pages?

    Close all tags that you've opened in the same order and same case. Must conform to strict rules of XML when being parsed. Prior to IE9 would just render as html.

    • Are there any problems with serving pages as application/xhtml+xml?

      Browser MAY parse the document as XML? Microsoft® Internet Explorer only supports XHTML if it is served with MIME media type text/html rather than the recommended application/xhtml+xml.

  • How do you serve a page with content in multiple languages?

    If a resource exists in multiple languages, the web server can choose which variant it serves based on the Accept-Language header delivered by the browser.

  • Can you use XHTML syntax in HTML5? How do you use XML in HTML5?

    Yes. It can parse either HTML or XHTML and not choke. Match the mime-type of the content you're serving. use HTML syntax when sending pages as text/html use XHTML syntax when sending pages as application/xhtml+xml

  • What are data- attributes good for?

    Storing properties on a DOM element to be accessed at a later time. or Embedding custom non visible data to your HTML.

  • 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?

    DOM APIs ? Discuss w/ Sam

  • Describe the difference between cookies, sessionStorage and localStorage.

    ? Discuss w/ Sam

JS-Specific Questions

  • Which JavaScript libraries have you used? = jQuery, Underscore, Backbone - Sub Mootools, Prototype

  • How is JavaScript different from Java?

  • 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:

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?

    • Bonus points for the funny answer: "no one can"
    • Extra bonus points if they take a stab at explaining it
  • When would you use document.write()?

    • Correct answer: 1999 - time to weed out the junior devs
  • 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, and if so, what/how?

  • Explain "hoisting".

  • What is FOUC? How do you avoid FOUC?

  • 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:

[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?

JS-Code Examples:


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" if intially window.foo was false, undefined or zero else 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

jQuery-Specific Questions:

  • Explain "chaining".

  • What does .end() do?

  • How, and why, would you namespace a bound event handler?

  • 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:

$(".foo div#bar:eq(0)")

$('#bar:eq(0)') or $('#bar')

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 the differences between the IE box model and the W3C box model?

  • 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 screenreaders)?

  • Have you ever used a grid system, and if so, what do you prefer?

  • Hav you used or implement 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 LESS?

  • How would you implement a web design comp that uses non-standard fonts? (avoid mentioning webfonts so they can figure it out)

  • 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.

  • Tell me your favorite parts about Firebug / Webkit Inspector.

  • 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
  • This should make the laugh and is a fine way to relieve some tension at the end of the interview.

  • 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.