/Front-end-Developer-Interview-Questions

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

#JOB INTERVIEW QUESTIONNAIRE

@version 1.0

##Contributors

@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 (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 primary 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?
  • If you could master one technology this year, what would it be?
  • Explain the importance of standards and standards bodies.

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:
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".
  • 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?
  • 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

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

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.