Comments on: JavaScript interview questions

By: Robert

Robert — Sun, 20 May 2012 20:40:32 +0000

I noticed most folks used the map function for the string manipulation, whereas I went for array methods like Christian L for the browsers from Redmond.

var str = 'The quick brown fox jumps over the lazy dog'
str = str.split(' ');
for (var i = 0, len = str.length; i &lt; len; i++) {
   str[i] = str[i] + (i + 1);
   str.join(&#039; &#039;);
}

No need to declare the length outside the loop. Having it declared inside still only gets executed once, like var i = 0. Also it’s more efficient to avoid string concatenation just to add spaces to the array indices. Passing a space as the argument for join accomplishes the same thing more efficiently.

By: CheckThisResume.com

CheckThisResume.com — Sun, 25 Mar 2012 00:13:38 +0000

//Replace the string “The quick brown fox jumps over the lazy dog”
//with the string “The1 quick2 brown3 fox4 jumps5 over6 the7 lazy8 dog9″
str=”The quick brown fox jumps over the lazy dog”;
str2=””;
str.split(‘ ‘).forEach(function(x){str2+=x+x.length+’ ‘});
alert(str2);

By: joe

joe — Tue, 07 Feb 2012 21:05:32 +0000

“The quick brown fox”split(” “).map(function(e){
return e+(++i);
});

By: Christian L

Christian L — Sun, 20 Nov 2011 21:24:08 +0000

***Replace the string “The quick brown fox jumps over the lazy dog” with the string “The1 quick2 brown3 fox4 jumps5 over6 the7 lazy8 dog9”.***

var str = "The quick brown fox jumps over the lazy dog";
var str2 = str.split(" ");
 
var len = str2.length;
    for (var i = 0; i &lt; len; i++){
     str2[i] +=  (1 + i) + " "
    }
 
str2 = str2.join("");

By: Alexander

Alexander — Sun, 11 Sep 2011 19:28:01 +0000

Fair, fair

now i know that i’m not a javascript developer… yet :p

By: Gareth Elms

Gareth Elms — Sun, 07 Aug 2011 16:15:27 +0000

Really enjoyed going through these. More…!

By: alpha123

alpha123 — Thu, 28 Jul 2011 19:09:55 +0000

If I was interviewing someone for a JavaScript position, I’d probably just have them write a basic CSS selector engine. Difficult, but fun. I’ve written 3. 😛 Usually doesn’t take more than a day or two to have something working well.

Oh, and here’s my slightly hackish #9:

'The quick brown fox jumped over the lazy dog'.split(' ').reduce(function (p, c, i) { return (!+p ? p + ' ' : '') + c + (i + 1) }, 1)

By: GDmac

GDmac — Sun, 24 Jul 2011 13:51:31 +0000

I like the PHP explanation of the comparison types (i.e. equal vs. identical)
( http://www.php.net/manual/en/language.operators.comparison.php )

"1" == 1; // Equal
"1" === 1; // Identical

By: Sergio Cinos

Sergio Cinos — Sun, 17 Jul 2011 04:41:53 +0000

Great questions! I usually interview JS engineers at my current job, so probably I’ll use some of them :). Here are my thoughts about some questions:

#2 – Good one, most people miss undefined and null.

#3 – Good one. I’d add the usual closure created inside a loop and trying to use the loop index.

#4 – Good. Using eval is a total fail for the candidate.

#5 – Ok. Not using an anonymous function is a total fail.

#6 – I think Array.prototype.reduce is a better choice. You have to deal with empty initialValue, that is very tricky. If the candidate’s implementation doesn’t match the Spec completely (specially for corner cases), it’s ok, but I’ll show the spec to the candidate and ask for a full implementation (let’s check if the candidate can read and implement a spec). BTW, all solutions provided in previous comments lack type checking (double fail: it is in the spec and omit type checking is a very bad practice).

#11 – Just replace &. Changing %22 is a bad (you are mixing url encoding and html encoding).

#12 – Not JavaScript, I don’t care if a JS Engineer doesn’t know about it.

#13 – I don’t care if a JS Engineer doesn’t know about how to implement something in jQuery. I expect him to be able to discuss about jQuery good features vs. bad features, and build his own framework/library.

By: Garrett

Garrett — Sun, 10 Jul 2011 18:24:40 +0000

Surprised seeing so many getting the answer to question 1 wrong! And when I see a question whose answer is “implementation dependent” or “nonstandard”, I worry that the interviewer might have the wrong answer.

So here’s the deal with parseInt.

ECMAScript 3 discourages octal interpretation but allows it; so the answer is “implementation dependent — don’t expect a consistent result from parseInt(‘010’);”

When radix is 0 or undefined and the string’s number begins with a 0 digit not followed by an x or X, then the implementation may, at its discretion, interpret the number either as being octal or as being decimal. Implementations are encouraged to interpret numbers in this case as being decimal.

Says that octal is optional.

ES5 banned the octal interpretation allowance mistake. The function parseInt no longer allows implementations to treat Strings beginning with a 0 character as octal values:

The parseInt function produces an integer value dictated by interpretation of the contents of the string argument according to the specified radix. Leading white space in string is ignored. If radix is undefined or 0, it is assumed to be 10 except when the number begins with the character pairs 0x or 0X, in which case a radix of 16 is assumed. If radix is 16, number may also optionally begin with the character pairs 0x or 0X.

But web browsers c2011 are not caught up to the new spec — Firefox 5 and Safari 5 parse octal when no radix is specified, in violation of ECMAScript 5.

parseInt("010"); // A result of '8' is a violation of ES5

I’ve updated MDC docs for parseInt regarding octal interpretation in ES3 and how it is forbidden in ES5.
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseInt