Pro Javascript Programmer Interview Questions (with Answers)

April 21, 2024 Post a Comment

What are good questions to determine if applicant is really a pro JavaScript (browser side) developer ? Questions that can distinguish if someone is not an ad-hoc JavaScript progra

Solution 1:

Because JavaScript is such a small language, yet with incredible complexity, you should be able to ask relatively basic questions and find out if they are really that good based on their answers. For instance, my standard first question to gauge the rest of the interview is:

In JavaScript, what is the difference between var x = 1 and x = 1? Answer in as much or as little detail as you feel comfortable.

Novice JS programmers might have a basic answer about locals vs globals. Intermediate JS guys should definitely have that answer, and should probably mention function-level scope. Anyone calling themselves an "advanced" JS programmer should be prepared to talk about locals, implied globals, the window object, function-scope, declaration hoisting, and scope chains. Furthermore, I'd love to hear about [[DontDelete]], hoisting precedence (parameters vs var vs function), and undefined.

Another good question is to ask them to write a sum() function that accepts any number of arguments, and returns their sum. Then, ask them to use that function (without modification) to sum all the values in an array. They should write a function that looks like this:

functionsum() {
  var i, l, result = 0;
  for (i = 0, l = arguments.length; i < l; i++) {
    result += arguments[i];
  }
  return result;
}
sum(1,2,3); // 6

And they should invoke it on your array like this (context for apply can be whatever, I usually use null in that case):

vardata = [1,2,3];
sum.apply(null, data); // 6

If they've got those answers, they probably know their JavaScript. You should then proceed to asking them about non-JS specific stuff like testing, workflows, version control, etc. to find out if they're a good programmer.

Solution 2:

Basic JS programmming

Scope of variable
What is Associative Array? How do we use it?

OOPS JS

Difference between Classic Inheritance and Prototypical Inheritance
What is difference between private variable, public variable and static variable? How we achieve this in JS?
How to add/remove properties to object in run time?
How to achieve inheritance ?
How to extend built-in objects?
Why extending array is bad idea?

DOM and JS

Difference between browser detection and feature detection
DOM Event Propagation
Event Delegation
Event bubbling V/s Event Capturing

Misc

Graceful Degradation V/s Progressive Enhancement

Solution 3:

(I'm assuming you mean browser-side JavaScript)

Ask him why, despite his infinite knowledge of JavaScript, it is still a good idea to use existing frameworks such as jQuery, Mootools, Prototype, etc.

Answer: Good coders code, great coders reuse. Thousands of man hours have been poured into these libraries to abstract DOM capabilities away from browser specific implementations. There's no reason to go through all of the different browser DOM headaches yourself just to reinvent the fixes.

Solution 4:

Ask them how they ensure their pages continue to be usable when the user has JavaScript turned off or JavaScript isn't available.

There's no One True Answer, but you're fishing for an answer talking about some strategies for Progressive Enhancement.

Progressive Enhancement consists of the following core principles:
basic content should be accessible to all browsers
basic functionality should be accessible to all browsers
sparse, semantic markup contains all content
enhanced layout is provided by externally linked CSS
enhanced behavior is provided by [[Unobtrusive JavaScript|unobtrusive]], externally linked JavaScript
end user browser preferences are respected

Solution 5:

Ask how accidental closures might cause memory leaks in IE.

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