Here's where Firebug comes in with its JavaScript debugger. I'm used to using a debugger in every language I deal with, so using Firebug is a no brainer. Since it supports breakpoints, stopping execution and inspecting local variables and the rest of the scope generally beats alerts and console.logs for me.

Here's what a typical breakpoint looks like in Firebug:

It's easy to set breakpoints in static scripts – just open the Scripts tab, select a JavaScript file from the dropdown menu, and click to the left of the wanted line number.

Then, when the page is reloaded, if your breakpoints are triggered, Firebug will pause script execution and transfer the control to you.

In most cases, the method above is the only method of setting breakpoints you will ever need to use.

The Problem With Dynamic JavaScript

However, what if the JavaScript file where you need to set breakpoints is not static but instead dynamic (generated on the fly). If you set a breakpoint in this case and reload the page, the breakpoint will most likely disappear, especially if the JavaScript url is generated uniquely every time.

The Solution

If you have access to the source, the solution comes in the form of the

debugger;

keyword. Just add it to your dynamic JavaScript generator or into any JavaScript file you have access to exactly where you want Firebug to break, and voila – it does.

More so, this method also works in Google Chrome and IE (if you have Microsoft Script Debugger). Here is a screenshot of my Chrome Beta 4.0.266.0 triggering:

I consider this feature relatively unpublished and therefore awesome because:

• it's hard to search for this specific meaning of the keyword "debugger" when Firebug itself is a debugger and it's a very popular word
• nobody really reads documentation for Firebug, and even if they do, I haven't actually seen the debugger keyword mentioned
• I didn't know about it until recently, even though I've been using Firebug for years

Of course, you need access to the code for this to work, so it's not going to work if you're trying to debug someone else's JavaScript.

And finally, don't forget to remove any traces of 'debugger' from your code when you go live or your users will rightfully hunt you down.

Credits And References:

• suggested by a co-worker from Plaxo – Russ. Thanks Russ!
• some more interesting info at StackOverflow and Infragistics.

Happy debugging!

(*) – if your project works 100% on the first pass, you must be either a magician or Jon Skeet (Jon Skeet Facts – a-la Chuck Norris, a must read).

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Debugging on the client side with -v didn't help much:

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artem@DeathStar:~/svn/b2/Fetch/LinkChecker> ssh -v monkey@192.168.1.30
OpenSSH_4.6p1, OpenSSL 0.9.8e 23 Feb 2007
...
lots of boring shit
...
debug1: Found key in /home/artem/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
...
more boring shit
...
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Offering public key:
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Offering public key:
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Offering public key: /home/artem/.ssh/id_rsa
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Trying private key: /home/artem/.ssh/id_dsa
debug1: Next authentication method: keyboard-interactive
Password:

After breaking my head over possible reasons why the pile of junk that thinks it's smarter than me next to my feet doesn't work, kicking it a few times, and observing the same result, I turned to debugging the ssh daemon itself – sshd.

• The -d option disables the daemon mode and enables debug mode, in which only 1 connection is accepted for the lifetime of the server, after which it simply quits.
• -dd simply enables a more detailed output.
• -e switches this debug output from a log file to STDOUT.

However, to free up port 22, I had to stop the daemon that was already running, or else a "Bind to port 22 on 0.0.0.0 failed: Address already in use." error appeared (duh). An interesting question though, especially for people doing this to remote boxes, what happens when one stops sshd? Ever thought of doing that but instead ran over to your mommy crying like a little girl? Well, fear no more, because I'll tell you exactly what happens:

1. New users will have their connection refused.
2. Your own connection will not be interrrupted. sshd works by spawning a new instance of itself for every incoming connection, so your own sshd process will stay in memory.

So where was I?

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/usr/sbin/sshd -dd -e

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...
Authentication refused: bad ownership or modes for directory /home/monkey
...
Failed publickey for monkey from 192.168.1.30 port 56287 ssh2

AhA!! (emphasis on the last 'a'). What have we here?

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artem@DeathStar:~> cd /home/
artem@DeathStar:/home/> l
drwxrwx--- 29 monkey  users 4096 2008-08-06 23:14 monkey/
 
DeathStar:/home/ # chmod 755 monkey
drwxr-xr-x 29 monkey  users 4096 2008-08-06 23:14 monkey/
 
artem@DeathStar:~/svn/b2/Fetch/LinkChecker> ssh -v monkey@192.168.1.30
OpenSSH_4.6p1, OpenSSL 0.9.8e 23 Feb 2007
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.1.30 [192.168.1.30] port 22.
debug1: Connection established.
debug1: identity file /home/artem/.ssh/id_rsa type 1
debug1: identity file /home/artem/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.6
debug1: match: OpenSSH_4.6 pat OpenSSH*
...

Connection established, all systems are go, the key has been accepted.

Inspired by http://linux.derkeiler.com/Mailing-Lists/Fedora/2005-08/1105.html

P.S. Don't forget to /etc/init.d/sshd start.

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