JavaScript interview questions

07 Jun 2011

The questions below were asked in a preliminary check before the actual interview. The role itself was for a “JavaScript Engineer”. This particular set of questions is from a job I applied to over a year ago. I’ve chosen to share them here because I think readers of this blog would benefit from knowing what kind of things are expected if you’re applying to a JavaScript-centric role.

What is the relationship between ECMAScript, Javascript and Jscript?
What core types are available in Javascript?

What do the following statements return and why?

parseInt("07");
parseInt("09");
parseInt("010");
 
"1" + 2 + 3;
3 + 2 + "1";
 
"1" == 1;
"1" === 1;
"1" == true;
"1" === false;

Alert the contents of the bar variable using the foo variable
var foo = "bar"; var bar = "foobar";
Alert the string “foobar” after a 10 second delay.
Implement Array.prototype.filter for IE.
Create a Person class with public/private/privileged members and methods.
Why does the statement 5 * 1.015 not return 5.075?
Replace the string "The quick brown fox jumps over the lazy dog" with the string "The1 quick2 brown3 fox4 jumps5 over6 the7 lazy8 dog9".
List several ways that you can communicate asynchronously with the server.
How would you embed this URL in a link inside an XHTML document?
http://www.google.com/search?hl=en&q=%22xhtml%22
How would you serve a StyleSheet only to IE users older than IE8?
Write a jQuery plugin to display a list of images in a Lightbox.

What do you think of these questions? Fair?

Thanks for reading! Please share your thoughts with me on Twitter. Have a great day!

So far there's been 49 Responses to
“JavaScript interview questions”

Graham B June 7th, 2011 at 6:53 pm

Mostly fair, though I’d say there’s a bit of a skill gap between a timeout alert and writing OOP with privileged members. But maybe that’s intentional 🙂 Also if I were the interviewer I’d try to avoid specifying the framework, but again it all depends on the scenario.
Misha Reyzlin June 7th, 2011 at 6:57 pm

Questions seem to be fair and interesting enough, though some things here require quite too much time for an interview, aren’t they?

Also, for the purists, it would be a good idea to write a tiny comment “yes, we know that this is not an actual class, but JS implementation of such”.

Also, quirks of XHTML are kinda dated, while knowing them may show the natural curiosity – it’s natural enough that even very good dev will not have direct experience with them. If already, it’d be better to ask something pure XML related, not XHTML / validation type question.
Corey Hart June 7th, 2011 at 6:58 pm

Is it typical to use anything but radix 10/16 in development? And as long as your allowed to say “because javascript is retarded that way” for some of the Why’s, it looks good.
Dan G. Switzer, II June 7th, 2011 at 7:02 pm

I’d argue that the question:

“How would you serve a StyleSheet only to IE users older than IE8”

Really isn’t a JS question at all, because I’d expect you to use IE conditional comments.
Ross Hadden June 7th, 2011 at 7:08 pm

They all seem very fair, ranging from very basic to mildly advanced. I’m a little confused on the Alert the contents of the bar variable using the foo variable question. I feel like it should be a simple answer (possibly because it was near the beginning of your list, whatever significance that has), but it was the one question that has me stumped.
Aaron June 7th, 2011 at 7:15 pm

Not fair. Given that most of these answers can be found in seconds via google, these test will quantify the user’s ability to answer test questions, not demonstrate and understanding of the fundamentals.

IMO, tests are an outdated concept for hiring a developer/engineer. A test places the developer into an environment at right angles to the environment in which they will be working.

In a test environment, they have to solve rapid fire tests about theoretical constructs in a severely shortened period of time. In real life environment, an engineer solves a set of interconnected tests about practical constructs, over several days or weeks.
Kevin Major June 7th, 2011 at 7:19 pm

For those of us who are novices, what would the correct answers be?

Mathias Bynens June 7th, 2011 at 7:20 pm

I have a feeling this is not the right way to do it:

var i = 0;
"The quick brown fox jumps over the lazy dog with a spoiler".replace(/ |$/g, function(a) {
  return ++i + a;
});

What am I missing here?

Boiss June 7th, 2011 at 7:47 pm
I have something similar from Mathias, not sure if there is another way to get the index, my code is :
var i=1;"The quick brown fox jumps over the lazy dog".replace(/s|$/g,function(s1) { return (i++)+s1});
Doug June 7th, 2011 at 7:51 pm

Looks pretty good… now I know I’m not a JavaScript developer.

Graham B June 7th, 2011 at 8:08 pm

@Ross Hadden – this?

var foo = "bar";
var bar = "foobar";
alert(window[foo]);

Jamie June 7th, 2011 at 8:15 pm

“Write a jQuery plugin to display a list of images in a Lightbox.”

I hope the right answer is, “why on earth would I do something that’s been done a hundred times before?”

At least, if I had a programmer faced with a need for a lightbox, I’d kill him if he wrote it himself…

Eli Perelman June 7th, 2011 at 8:22 pm

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

Ihab Khattab June 7th, 2011 at 8:44 pm
@Graham B

Or may be @Ross Hadden thought like me :
alert(eval(foo));
I didn’t think it’s that tricky 🙂

TiTi June 7th, 2011 at 9:46 pm

Thank you for sharing thoses questions.
I also think it’s a good idea to share answers because I’m usually really pissed when there is only questions, not answer in such article, and it’s sometimes not easy to find the good answer(s). So here are my answers as I would respond the day of the interview :

#1.
ECMAScript = Define various detailled specs
Javascript = The language, general word
Jscript = A Microsoft implementation

(please don’t ask more :-p)

#2.
Boolean
Number
String
Date
Object?

(after a rapid search it seems the 2 last are wrong)

#3.

parseInt("07"); // -> 7
parseInt("09"); // -> 9? Hum i known there something with 08 / octal base
// I also know second parameter of parseInt (base) is very important, typically 10 for most conversions.
parseInt(”010”); // -> 10?

[ok wrong for the 2 last again, and i really don’t care why.
I just know that it works if you set the second argument to 10. Fuck it. Damn binary-octal-stupid parser^^]

"1" + 2 + 3; // -> "123" because of concatenation and `type priority` ; "1" + 2 = "12" ; "12" + 3 = "123"
3 + 2 + "1"; // -> "51" ; 3 + 2 = 5 ; 5 + "1" = "51"

Do I just invented `type priority` ? Anyway i think i’m right even if i don’t know the real name used for the inner workings.

"1" == 1; // -> true
"1" === 1; // -> false (value &amp; type checked)
"1" == true; // -> true (because "1" == 1)
"1" === false; // -> false

#4.

alert(eval(foo)); // eval is evil
</p>
 
#5.
 
<pre lang="javascript">
setTimeout(function()
{
	alert("foobar");
}, 10000); // after a minimum of 10 seconds [likely a few ms after 10s passed]

#6.

uh I don’t really know it doesn’t exist in IE, I’m relying on higher level frameworks usually….
I guess something like (sorry, comment system broke the indentation):

if(!Array.prototype.filter)
{
	Array.prototype.filter = function(search)
	{
		var matches = [];
		for(var i = 0, len = this.length; i<len; i++) // yeah i know while(i--) stuff is better, also a little more obscure
		{
			if(this[i].toString().indexOf(search) != -1) // toString(), nope?
			{
				matches.push(this[i]);
			}
		}
		return matches;
	}
}
 
// Please don't hit me if this is a bad implementation, but help me with a better one (and comments!).

#7.

// This one is &quot;easy&quot; for me because i worked the question a few months back
// It&#039;s think it&#039;s an important question and the following model is not enough mentionned
 
function Person()
{
	this.publicMember = "foo";
 
	this.privilegedMethod = function()
	{
		return privateMethod();
	}
 
	var privateMember = "bar";
 
	function privateMethod()
	{
		return "hello";
	}
 
}
// Public methods
Person.prototype = 
{
	getDate: function()
	{
		return new Date();
	},
	getWorld: function()
	{
		return "world";
	}
}
// Bonus: Public static method
Person.kill = function()
{
	return "dead";
}
 
 
// (I think the closure way to get private stuff is more known, but I prefer this one :-p)
// And I guess questions on .prototype, performance, closure and stuff like that could be interesting.

#8.

5 * 1.015 != 5.075 because of the way floats are stored internally (?+?+mantisse). Its an approximation. Leads to small variations when doing maths. Be really really careful for financial calculations!!

#9.

*Challenge accepted*

//First draft:
 
var tab = &quot;The quick brown fox jumps over the lazy dog&quot;.split(&quot; &quot;);
var out = &quot;&quot;;
for(var i = 0, len = tab.length; i&lt;len; i++)
{
	out += tab[i] + (i+1);
}
out; // WRONG: forgot spaces
 
 
//Second draft:
 
var space = " ";
var tab = "The quick brown fox jumps over the lazy dog".split(space);
var out = "";
for(var i = 0, len = tab.length; i<len; i++)
{
	out += tab[i] + (i+1) + space;
}
out; // WRONG: one more space at the end
 
 
//Third draft:
 
var tab = "The quick brown fox jumps over the lazy dog".split(" ");
for(var i = 0, len = tab.length; i<len; i++)
{
	tab[i] += (i + 1);
}
tab.join(" "); // RIGHT, and elegant enough for me

Dammit I forgot the replace method could take a function as second argument.
Hum wondering about perfs… Depending on string length, targetted browsers, …

#10.

-AJAX (XmlHttpRequest)
-Using flash & communication between flash and your javascript & flash remote connection

// And thoses which look terrible to me
-Creating a new element such as ,,
-Changing an iframe src
-AJAX with long polling (for server -> client)
[-page reload / change page location]

#11.

link
But I guess I’m missing the point.
Inside another link ?
link
I got a very bad feeling, this is way more complicated ^^

#12.

[meh, comment system is really broken on this one ; had to use < and > by myself]

<!– if [ IE < 8 ] –>
<style type="text/css" src="iefail.css" />
<!– [ endif ] –>

(i'm sure this is not exactly thoses chars but the idea is here)
(by the way i prefer NOT to use a separate stylesheet, also might be useful in some radical design decision ; and what about server sniffing to provide a different ?)

#13.

(function($)
{
	$.fn.lightBox = function()
	{
		//...
		return this.each(function()
		{
			var $this = $(this);
			$this.css('border', '1px solid red');
			$this.click(function()
			{
				//...
			});
 
			//....
		});	
	}
})(jQuery)

I think thoses questions cover some important concepts.
It is also not simple true/false questions, candidate has to write code, wich is also (very) important.
But could you judge someone javascript level in 13 questions ?
Depends a lot what your expecting:
write low level stuff / frameworks, or high end code ?
js guru ? someone with basics that will rapidly progress ?
…

Cheers++

TiTi June 7th, 2011 at 9:55 pm

Because of comment system issues, here is what’s missing:

#10.

-Creating a new element such as <script>,<img>,<iframe>

#11.

http://pastebin.com/M6yimsJL

(comment system html encoding is a real nightmare)

#12.

…and what about server sniffing to provide a different <head>)
Seamus June 7th, 2011 at 10:09 pm

This list looks great.

You could ask them to describe how they would write a serialize and deserialize (encode/decode) methods in native JavaScript. This would tell you how well they know could use Array methods join and splice.

Lea Verou June 7th, 2011 at 11:20 pm

My first thought for the fox one was:

"The quick brown fox jumps over the lazy dog".split(' ').map(function(word, i) { return word + (i+1) }).join(' ');

SztupY June 7th, 2011 at 11:24 pm

I was thinking about alert(eval(foo));
Lea Verou June 7th, 2011 at 11:25 pm

Btw, how do you post the syntax highlighted snippets? James, your blog hates me 😛
Sami Samhuri June 8th, 2011 at 5:15 am
I wrote the same code quote for quote, but minus the trailing semi. Lispy JS ftw.
"The quick brown fox jumps over the lazy dog".split(' ').map(function(w,i){ return w + (i + 1) }).join(' ')
Anyway I think the questions are pretty fair, agree with Graham that specifying the framework is odd, but whatever. jQuery is so common that it’s weird if you don’t know even a little, if you have a web background.

Splurov June 8th, 2011 at 6:19 am

Lea, it’s WP-Syntax plugin:

<pre lang="javascript">"The quick brown fox jumps over the lazy dog".split(' ').map(function(word, i) { return word + (i+1) }).join(' ');</pre>

Steve Antal June 8th, 2011 at 6:25 am

These questions stand out:

> How would you embed this URL in a link inside an XHTML document?
> How would you serve a StyleSheet only to IE users older than IE8?

XHTML has nothing to do with JS, also it’s deprecated there is no real point using it.

About the second: if you want to ask people IE and JS related stuff you can ask them about event handling, AJAX techniques, JSON but CSS I don’t think is related, unless of course the correct answer is loading the CSS via JS with your IE detection code. 😀
Mark McDonnell June 8th, 2011 at 9:23 am
I assume this is the correct way of replacing the string…
var counter = 1; "The quick brown fox jumps over the lazy dog".replace(/([a-z])b/gi, function(str, cg1){ return cg1 + (counter++); });
I had a go at ‘Implement Array.prototype.filter for IE’ but because I haven’t ever used that Array method before I had to lookup the specs on MDN as to what it actually needed to do (so not knowing would probably mean I failed).
fwolf June 8th, 2011 at 10:06 am

@ Steve Antal: Since when is XHTML suddenly be deprecated?
Better get of that drugs ASAP 😉

cu, w0lf.
Ross Hadden June 8th, 2011 at 1:17 pm

@Graham B: Thank you, I was right I was overlooking something very easy. Immediately after posting I realized I could do what @Ihab Khattab suggested, however your way felt sooo clean after rolling in the dirt that is eval().

Thank you!
Ihab Khattab June 8th, 2011 at 2:13 pm
@Graham B
@Ross Hadden

agree with you

A friend of mine suggested using this instead of window 🙂
alert(this[foo])
Thor Larholm June 8th, 2011 at 2:35 pm

Hi guys,

I wrote these interview questions back in 2009.

As James mentions, the position was for a Javascript Engineer to work with a team of 10-12 people. At the time, it was 600KB+ OOP JS (a lot less minified/gzip’ed) targetting the usual IE7+/Firefox3+/Chrome/etc set.

The questionnaire was meant as a preliminary check that a prospective consultant could fill out before the actual interview.

I wrote a graded answer guide next to the questionnaire, perhaps I should dig it out from my archives. Nobody scored 100%, but that didn’t matter.

It helped to establish a baseline of competency and areas of interest without going into too much detail, which is why it covers both novice and intermediate areas along with some open-ended questions.

I’m glad to hear that most of you think the questions were fair. To be honest, I wouldn’t use the same question sheet today; It was specific to the team needs and quite a lot has changed since then.
Katie June 11th, 2011 at 1:53 am

I would walk out of the interview if presented with these questions. If a job presented this as a preliminary questions prior to the interview, I wouldn’t bother to apply.

The questions leave me a bad taste about the position. I cannot put my finger on why; it may be the basic level of the questions. Those questions are not in-depth enough to judge whether someone truly knows javascript beyond the basics and parroting back what they were told was ‘good’. Questions about prototypal inheritance, favorite framework and why, patterns, etc would be much more approriate.

Robby Pelssers June 14th, 2011 at 9:52 pm

My one_liner to tackle the fox transformation:

var statement = "The quick brown fox jumps over the lazy dog";
var statement_new = statement.split(' ').map(function(word, index) {
  return word + index;
}).join(' ');

Robby Pelssers June 14th, 2011 at 10:08 pm

Regarding the foo bar question:

var foo = "bar";
var bar = "foobar";
var theName = "";
for (name in this) {
  if (this[name] == foo) {theName = name;}
}
alert(theName + foo);  //should alert "foobar"

patrick June 15th, 2011 at 3:16 am

if you really care about the skill of appliers, check their commits to opensource projects
Thor Larholm June 15th, 2011 at 10:00 am

Katie, you would be surprised by how many people who classified themselves as Javascript Experts that questionnaire filtered out.

As mentioned, it helped to establish a baseline of competency and areas of interest without going into too much detail. That was quite deliberate, it was not meant to judge whether someone truly knows Javascript.
Mark June 15th, 2011 at 1:36 pm
As far as the foo/bar question, there wasn’t any mention as what should happen with the foo variable so I just simply did…
var foo = "bar"; var bar = "foobar"; foo = bar; alert(foo); // foobar
Kim June 17th, 2011 at 10:37 am

@TiTi Thanks for sharing your answers

@James I think it’s was a very good idea to share these interview questions, you probably helped some self called ‘JavaScript Experts’. And even the author seems interested in the comments (-:
Half Marathon June 25th, 2011 at 9:45 pm

Some of these questions are useful, but some like the first part of 3 I would not use.

Mike July 6th, 2011 at 12:16 am

1. a) ECMAScript is the spec for JavaScript and another name for JavaScript
b) JavaScript is an implementation of the ECMAScript language standard and is primarily used to manipulate the DOM
c) JScript is a JavaScript dialect MS created

2. Core types: Number, String, Boolean, undefined, null

3. Statement Evaluations:

// only "07" yield the expected 7, base/radix 8 is the default
// to get around this always specify base 10: parseInt("09", 10)
parseInt("07") // = 7 because 7 radix 8 is 7
parseInt("09") // = 0
parseInt("010") // = 8
 
"1" + 2 + 3; // type priority is given to string all the way, yields "123"
3 + 2 + "1"; // type priority is given to number then string, yields "53"
 
"1" == 1; // value evaluation only, yields true
"1" === 1; // value and type evaluation, yields false
"1" == true; // "1" as boolean is true, value evaluation only, yields true
"1" === false; // value and type evaluation, yields false

4. Alert contents of bar using foo

var foo = "bar", bar = "foobar";
// this is similar to eval("bar") which tries to evaluate the `bar` variable
// and therefore yields `bar`s value of "foobar"
alert(eval(foo));

5. Alert “foobar” after 10 seconds

// use set timeout timer to execute a function after 10 seconds or 10000 ms
setTimeout(function() {
    alert("foobar");
}, 10000);

6. Implement Array.prototype.filter for IE.

// from http://stackoverflow.com/questions/2790001/fixing-javascript-array-functions-in-internet-explorer-indexof-foreach-etc/2790686#2790686
if (!('filter' in Array.prototype)) {
    Array.prototype.filter= function(filter, that /*opt*/) {
        var other= [], v;
        for (var i = 0, n = this.length; i &lt; n; i++)
            if (i in this &amp;&amp; filter.call(that, v = this[i], i, this))
                other.push(v);
        return other;
    };
}

7. Create a Person class with public/private/privileged members and methods.

// I like TiTi's solution for this in the previous comment
// https://j11y.io/javascript/javascript-interview-questions/#comment-33779
function Person()
{
    this.publicMember = "foo";
    this.privilegedMethod = function() {
        return privateMethod();
    }
    var privateMember = "bar";
    function privateMethod() {
        return "hello";
    }
}
// Public methods
Person.prototype = {
    getDate: function() {
        return new Date();
    },
    getWorld: function()
    {
        return "world";
    }
}

8. Why does the statement 5 * 1.015 not return 5.075?

JavaScript uses a floating-point number format which cannot store certain numbers “exactly”. In other words, some numbers are approximations. To get precise decimal places use toFixed or Math.round

5 * 1.015 // 5.074999999999999
parseFloat((5 * 1.015).toFixed(3)) // 5.075
parseFloat(Math.round((5 * 1.015) * Math.pow(10,3)) / Math.pow(10,3)) // 5.075

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

// there are several ways to do this, 
// .split or .replace both have good solutions to this
 
// .replace
var i = 1,
    fox = "The quick brown fox jumps over the lazy dog";
 
fox.replace(/w+/g, function(word) {
    return word + i++;
});
// .split
fox.split(' ').map(function(word, i) {
    return word + (i+1) 
}).join(' ');

10. List several ways that you can communicate asynchronously with the server.

– XMLHttpRequest – standard ajax call
– create new img, iframe, script elements with a src attribute
– update the src attribute on img, iframe, script

11. How would you embed this URL in a link inside an XHTML document?

http://www.google.com/search?hl=en&amp;q=%22xhtml%22

a) change & to &
b) change %22 to "

<a href="http://www.google.com/search?hl=en&amp;q=&quot;xhtml&quot;" rel="nofollow">&quot;XHTML&quot; google search</a>

result: "XHTML" google search

12. How would you serve a StyleSheet only to IE users older than IE8?

<!--[if lt IE 8 ]&gt;[stylesheet here]&lt;![endif]-->

13. Write a jQuery plugin to display a list of images in a Lightbox.

Don’t reinvite the mass produced wheel

Ivan July 8th, 2011 at 7:40 am
8.

I know that is not even the question… but the this a way to do it without using Math.round() or any thing like that:

Pretending that the number is always is given with 3 decimals:
String(1.015).replace(".","") * 5 /1000 //
Crisboot July 10th, 2011 at 6:10 pm

Nice, I’ll use some of them if you don’t mind 😀
Garrett July 10th, 2011 at 7:24 pm
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
Sergio Cinos July 17th, 2011 at 5:41 am

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.
GDmac July 24th, 2011 at 2:51 pm
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
alpha123 July 28th, 2011 at 8:09 pm
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)
Gareth Elms August 7th, 2011 at 5:15 pm

Really enjoyed going through these. More…!
Alexander September 11th, 2011 at 8:28 pm

Fair, fair

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

Christian L November 20th, 2011 at 10:24 pm

***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("");

joe February 7th, 2012 at 10:05 pm

“The quick brown fox”split(” “).map(function(e){
return e+(++i);
});
CheckThisResume.com March 25th, 2012 at 1:13 am

//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);
Robert May 20th, 2012 at 9:40 pm
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 < len; i++) { str[i] = str[i] + (i + 1); str.join(' '); }
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.

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