Which Tools are there for Code Comparison or Side by Side Comparing? How to Find Bugs in Javascript?

Though 99% of the code on our site is the work of 1 programmer, recently for the first time (and probably last) a programmer was hired to work on our site, he was given remote access to log in via ftp.

Background: He is located in a continent unknown to us, speaks a mothertongue that I cannot guesse from the English mails, and works in ways that are bit different than ours. It seems, this common workflow in long distant small projects where the original programmer is essential to update/customise their code.

Problem: The genius writes like a hacker, good quality but very poorly documented, some bugs occuring here or there. Now we are stuck with almost brilliant code with some bugs. Its Javascript开发者_如何学Python mainly.

Question: First of all 1. What ways/utilities/websites are there to find bugs in freshly delivered JavaScript code, when its difficult to understand parts of thes code to begin with? 2. What are good code comparison programs/utilities/websites sothat one can vew in parallel side by side comparison differences between two versions of code?

Obviously both are very related so hopefully there is one great tool on this planet that aims to combine bug finding as well as shows you the differences between versions.

Any suggestions are good answers to me as I have no clue where to start from here.

I agree with the posts above, Firebug for Firefox and Google Chrome/Chromium's Web Developer tools are great for most JavaScript debugging purposes. IE8 has an o-k set of Developer Tools. I'd only recommend using them if you're having issues in IE-only, otherwise, the previously mentioned tools will perform much, much better. If you really want to run the JavaScript through the error-checking and code-quality gauntlet, take a look at Douglas Crockford's JSLint.

It's also worth mentioning community-driven JSHint as a resource for testing JavaScript code. It's not as strict as JSLint and has better support for commonly-used JavaScript libraries.

The Windows applications listed above should work great for comparing files. If you're on OS X though, Kaleidoscope is a wonderful comparison app. It costs a little money, but it integrates very nicely with most versioning systems.

I agrre with @BiAiB, about the need for a code management/versioning tool - this will save you hours of heartache.

Another excellent file comparison tool is Beyond Compare - it truly is worth every penny that it costs (which is not much)

Probably the best tool to help in the discovery of what is happening in your JavaScript code is Firebug, a plug-in to Firefox. Google Chrome and IE have similar functionality, although each solution may lack feature (or have extra features) that the others don't.

And, I agree with everybody else - you need source control in a big way.

For file comparison tools, there is also the excellent and free WinMerge

Eclipse can do compare.

JsTestDriver is a wonderful testing tool.
But you will need to write unit tests for it.

A great tool is using firebug and the Webdeveloper toolbar plugins for mozilla firefox.