First, let’s get some basics out of the way.

• Comments and white-spaces are left in the code, increasing the payload size. I suggest using YUI Compressor before posting the code.
• Lines 1-3 – MooTools is included at the top of the script, PACKED. Thanks to PB Wiki’s Tests, we now know this is bad for client side performance. Stop doing this, see above!
• Lines 3-12 – They’ve included the FireBug Lite code to account for the 5 occurrences where they use console. Remove the 5 debug statements that don’t do squat and you can shave off ~350 bytes

Doing the above netted a 6940 bytes savings or a script 65% the size of the original (not to mention the client side cycles shaved off by removing the packed mootools). Click the link below to view it.

13048 Apr 21 00:17 sharethis_widget_better.js
19988 Apr 21 00:18 sharethis_widget_original.js

Digging into the code further I found a lot of various space saving things that could be done in the code (using radix in parseInt, avoiding at least one try catch block 83-89, etc). Also a few oddities like lines 329 – 332 (which looks like a bug), just asking for trouble by using _s in the global space, and wtf is going on with lines 460-464? Declaring _query to be [] then passing it to the ShareThis object, which from what I can tell doesn’t do anything, then setting the query property again to _query (which is really []) and then pointlessly setting a variable st to the newly created ShareThis.

I know I’m guilty of writing bad javascript also, but if you’re a company distributing a widget you should at least clean up the code a tad… ironically the ShareThis widget appears immediately after this line. =|