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What is the best parctice for debugging production javascript?

I have a Javascript SPA app, based on React, that it is about to go live.
In the app itself I log all Javascript exceptions and save them on the server for further debugging.
As my app will be minified I was wondering how I am to debug the stack traces I will get when a bug is hit.
I came across stacktracejs which looks promising, but the documentation looks a bit thin. So I was wondering if there is something better out there.
Just to clarify, coming from C world myself, I am essentially asking what is the equivalent to "GDB", where I can load the core a binary on it and start debugging.

You could use a library like source-map (If you can run nodejs on your server).
There you would load your source-map for the given file:
var smc = new SourceMapConsumer(rawSourceMap);
Then you would need to parse your stack trace extracting all line and column numbers. Those information you then can use to retrieve the original position.
console.log(smc.originalPositionFor({
line: 1,
column: 2
}));

Is there a way of downloading the whole of a webpage source in an HTML file?

I am using a WebRequest() function within the MetaTrader Terminal 4 codebase (MQL4) that allows one to download a HTML-response from a website.
Example site: http://www.forexfactory.com/docphoenix66#acct.57-tab.list
Here is an example how it is used in the MQL4 function call:
res = WebRequest( "GET",
"http://www.forexfactory.com/docphoenix66#acct.57-tab.list",
cookie,
NULL,
timeout,
post,
0,
result,
headers
);
and the documentation for the function WebRequest()
However, if I compare what is downloaded using a WebRequest() call with what you see when you right click and inspect element using Chrome or Safari, the bits I want available are missing!
In particular I want the trade information from below the following columns:
Instrument Price Open/Close Date Open/Close Lots Return
Profit Pips Chart Balance Swap Duration
And if you see below an example of what is missing from the htm file downloaded using the MQL4 function.
<td class="slidetable__cell slidetable__cell--fixed" style="width: 62px; min-width: 62px;"> <a id="snap_48205_trade_109309333" class="explorer__anchor explorer__anchor--trade"></a>
EUR/USD
</td>
If you download the HTML file, turn off your wifi and then open the file to see what was downloading, you see everything in the trade explorer still loading. Am I clear on what my problem is?

Short version: Yes, there is.
Long version: TL;DR;
Well, first, welcome to the Wild Worlds of MQL4
Given the intention is clear and given you were "promised" that there is "a possible way to read a HTML-page", I have to tell you it is not possible in all cases you will meet in real-world.
One may spend ages in MQL4-code domain to re-design html-sort-of Mark-Up syntax-(b)LOBs, suffering from all the restricted constraints the MQL4-code execution engine provided.
Nevertheless, the much faster, joyfull and a sure and future-proof ( read other posts on historically painfull creeping of the language syntax relief and crippled man*decades in API-integration code-base efforts ) approach exists .
Integrate MQL4-side via a professional fast & low-latency SIG/MSG-infrastructure with external, distributed processes, that can provide high-performance & robust services to MetaTrader Terminal ecosystem.
Using this approach we have prototyped and operate fast Mixed-Technical-and-Fundamental AI/ML-Inputs, including Web-page-feeds of Fundamental Data and News Announcements into the FX-trading realm 24/7/365 and it works blessingly well, independently of the limits the common MQL4 execution has.
If still in doubts, just try to read a page on rss.provider.com:6322/FED_actuals URL via a call to WebReqest() and you know, where is the dog burried.

Unminify / Decompress JavaScript

Original Question
This maybe a stupid question but is there a way in VS 2013 to unminify JavaScript?
Just making sure we are all on the same page here.
Minify:
var flashVer=-1;if(navigator.plugins!=null&&navigator.plugins.length>0){if(navigator.plugins["Shockwave Flash 2.0"]||navigator.plugins["Shockwave Flash"]){var swVer2=navigator.plugins["Shockwave Flash 2.0"]?"
That's just an example to make sure we all know what I'm on about. As far as I can tell there is no way to be able to do this. I have only been using VS 2013 for around 3 weeks so there is probably still stuff that is hidden to me.
If there is no way to do this within the program what is the next best thing for this?
I did see on another similar post that recommends the site http://jsbeautifier.org/ , so may have to give that ago but would make life easier if it was built into VS 2013
Thanks in advance as I know someone will be able to help me out here.
Update:
I have looked around VS 2013 and found nothing that can help me with this problem, like I said before they maybe some things I have missed (certain settings) so I guess if it cannot be done in VS what's the next best thing for the job? I seem to run into a fair amount of JS that is minifed and would like the quickest and best way to get the job done. I couple sites I have tried seem to have problems with it, is there a program I could install that would just allow me to short cut it with a hot-key or something. That would be pretty handy.
Update 2:
So I think its safe to say this cannot be done within VS2013, or for that matter at all due to missing var names and so on. So I have seen a few links and programs that allow you to format the code. Is there a way to do with within VS2013? And again if not what is the most reliable website/program that I can use to do this. Like I said I can see there have been answers and I appreciate all of them. I will be leaving this question open for a while to get more people to look at it and possibly give a better answer. Keep it up guys!
Update 3:
If anyone has any more information on this please do share. I am still looking around now and then waiting for someone to come up with something amazing for this. One day people.... One day!

The thing is that you cannot really "unminify" your code since some data was already lost - e.g. variable names. You can reformat it to more readable form though.
According to this question, since VisualStudio 2012 you can just use Ctrl+E, D keyboard shortcut
If the above is not right, there is this extension for VS 2010: http://visualstudiogallery.msdn.microsoft.com/41a0cc2f-eefd-4342-9fa9-3626855ca22a but I am not sure if it works with VS 2013
There is an extension to VisualStudio called ReSharper which can reformat javascript in a few different manners.
Also there are online formatters already mentioned in other answers (if your code is confidential, I would advise some paranoia manifested by downloading sources and using them locally).
Also you may always try to find unminified version of desired library on the interwebs
Also, there is the WebStorm IDE from JetBrains that is able to reformat JS - you may download a trial for the sole purpose of reformatting your minified scripts :)
If that's just to make debugging easier, you may want to use source maps
Also, here is a bunch of related questions:
How to automatically indent source code? <-- this is for VS2010, but it looks promising, maybe it will help you if it supports JavaScript (and it does since VS2012 according to MS support):
Ctrl+E, D - Format whole doc
Ctrl+K, Ctrl+F - Format selection
reindent(reformat) minimized jquery/javascript file in visual studio
Visual Studio 2010 can't format complex JavaScript documents
Visual Studio code formatter
how to make visual studio javascript formatting work?
I am not sure if they figured out a working way to reformat JS, but I've seen a few answers which might be helpful - I am just pasting this in here just FYI.
Added 03.06.2014:
http://www.jsnice.org/
This tool could be useful too, it even tries to infer minified names. As stated on their website:
We will rename variables and parameters to names that we learn from thousands of open source projects.

Personally I can't think of a reason to ever unminify code^:
If you're using a compiled js file (a-la google closure) and want more readable code to debug, use source maps available for well-supported libraries (speaking of jQuery, if it is served from a google CDN it already maps to the correct source)
If you're using a whitespace-only minified js file and want more readable code to debug, you could just toggle pretty print in-browser. This seems to best fit your question.
If you're using either of the above and want to modify the source code for a third-party js file, don't. Any future release will cancel out your change - instead consider one of the many patterns to extend a framework (or, perhaps, do some duck punching depending on the exact scenario.)
The other answers seem to cover the "unminification" process (maxification?) well, but it's worth making sure it's a necessary step first.
^ - Except when version control falls over, there are no backups and the only version of the file left is a minified copy in browser cache. Don't ask.

Its just a one way transformation .... sorry in normal cases you will not get something understandable back from minified JavaScript !
Make just a quick look at JQuery source for a second:
(function( window, undefined ) {
// Can't do this because several apps including ASP.NET trace
// the stack via arguments.caller.callee and Firefox dies if
// you try to trace through "use strict" call chains. (#13335)
// Support: Firefox 18+
//"use strict";
var
// The deferred used on DOM ready
readyList,
// A central reference to the root jQuery(document)
rootjQuery,
// Support: IE<10
// For `typeof xmlNode.method` instead of `xmlNode.method !== undefined`
core_strundefined = typeof undefined,
// Use the correct document accordingly with window argument (sandbox)
location = window.location,
document = window.document,
docElem = document.documentElement,
// Map over jQuery in case of overwrite
_jQuery = window.jQuery,
// Map over the $ in case of overwrite
_$ = window.$,
// [[Class]] -> type pairs
class2type = {},
// List of deleted data cache ids, so we can reuse them
core_deletedIds = [],
core_version = "1.10.2",
------
And now at the minify source:
(function(e,t){var n,r,i=typeof t,o=e.location,a=e.document,s=a.documentElement,
l=e.jQuery,u=e.$,c={},p=[],f="1.10.2", ....
I think now you see it =>
window => e
undefined => t
readyList => n
rootjQuery => r
core_strundefined => i
location => o
document => a
So its mapped somehow to make it more shorter look here to minify something
People normally use this so there is no way back
you can just format it look here

If the code has only been minified then the best you can do automatically is reformat to make it more readable. One way of doing this is using an online formatter/beautifier. E.g. Copy and paste the line of code you posted into http://jsbeautifier.org/ or http://www.jspretty.com/ and it'll produce something like this:
var flashVer = -1;
if (navigator.plugins != null && navigator.plugins.length > 0) {
if (navigator.plugins["Shockwave Flash 2.0"]
|| navigator.plugins["Shockwave Flash"]) {
var swVer2 = navigator.plugins["Shockwave Flash 2.0"] ? ""
But of course what these don't do is put any comments that have been removed by the minifier back in. And if the code has also been obfuscated then it will be a lot less readable since the variable names will have changed (e.g. var a instead of var flashVer). See here for further details.

As you can see from the other answers, there is no way to reconstitute minified Javascript back into its original form, it is a lossy compression. The best you can do is make it readable by reformatting it.
If the code is open source, then it is likely that the code will exists in a raw state on some form of version control site or as a zip. Why not just download the raw version if available?

There is an online tool to unminify Javascripts
http://jsbeautifier.org/
And also for CSS
http://mrcoles.com/blog/css-unminify/

How would I solve a coding puzzle with Javascript?

There is a website called Gild.com that has different coding puzzles/challenges for users to do. They can be completed in wide array of languages including Javascript. I am interested in solving these puzzles in Javascript, but I am unsure of the following:
How am I supposed to access the input file which is supposed to be passed as an argument?
How am I supposed to output the result?
My understanding of Javascript is that it is run from within an HTML page and that output really is only in the form of placing values in the HTML, modifying the DOM, etc. For that reason it is not clear to me how Javascript can be used for solving these types of problems. Can someone who has used Gild before or has some insights into my question suggest how to proceed?
An example of a problem would be: the given input file contains a positive integer, find the sum of all prime numbers smaller than that integer and output it.
EDIT: Some of the solutions below involve using external resources, but on Gild, I am supposed to put my solution in their editor and then submit it that way, like the following picture shows:
In other words, I don't think my solution can have access to Node.js or other external resources.
Edit: Here are some interesting articles that I have found that I think are the answer to my question:
http://www.phpied.com/installing-rhino-on-mac/
http://www.phpied.com/javascript-shell-scripting/

I haven't spent much time on Gild, but I do a lot of similar types of problems on Project Euler. I think the best way to go is probably Node.js.
If you're not familiar, Node is basically server-side JavaScript that runs in Google's V8 engine. Installing it on your own Mac/Windows machine takes about 2 minutes. It's also really fast (considering it's JavaScript).
And you'd use it like this:
var fs = require('fs'); // the filesystem module
var contents = fs.readFileSync('theFile.txt', 'utf-8');
// Do stuff with the file contents...
Everything after those first two lines can be done with the same JS you'd write in the browser, right down to calling console.log() to spit out the answer.
So, if you wrote your script in a file on your desktop called getprimes.js, you'd open up your terminal and enter node ~/Desktop/getprimes.js (assuming you're on a Mac)

If you're:
on a Mac,
planning to do a lot of these puzzles, and
willing to pay $10, then
I highly recommend CodeRunner. It encapsulates runtimes for a variety of languages — from C to JavaScript — and lets you quickly build and run any sort of one-off code. Just hack together your code, ⌘R, and the results are printed right there in the same window.
I haven't used any file-based JavaScript in CodeRunner, but I imagine kennis's suggestions would apply. To output your results:
console.log(...)
Easy as pie!

Can anyone de-obfuscate this exploit?

I came across the following exploit due to a warning from my AV software. It originated from an adserver delivering banner ads on one of my sites.
I have retrieved the content with Wget and copied to pastebin.
http://pastebin.com/m6fa38fac
[Warning: Link may contain malware - Do not visit from vulnerable PC.]
Please note that you have to scroll horizontally on pastebin as the code is all on one line.
Can anyone find out what the exploit actually does?
Thank you.

Not quite, as it includes (the equivalent of):
var mtime= new Date(document.lastModified).toUTCString().split(' ')[4].split(':');
it then uses the minutes and seconds of the last-modified time of the document containing it as a key to decode the array. If you can't still retrieve that javascript:alert(document.lastModified) time we'd have to brute-force it.
ETA: ah, actually it only uses the first digit of the minutes, and from the way it uses it we can guess it's supposed to be 1. That's leaves only sixty possibilities, and a quick loop reveals that meaningful javascript only comes out for 16 seconds.
I've put the decoded script here; it will probably also ping your anti-virus. Summary: it runs exploits against the Java, Flash and Acrobat plugins, running a payload from googleservice.net which is (surprise surprise) a Russian attack site.

This ussualy works to print de-obfuscated code
eval = alert;
in firefox with firebug, i solved it like this:
var lpsy16=lpsy;
eval = console.log; // This line was added
eval(lpsy+parseInt(gouy[0]));
Output is here:
--deleted due to zoidberg's comment--