Found this on AListApart.com
Monday, August 20th, 2007It was amazingly valuable for debugging JS.
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Safari also has a javascript debugger. You need to enable the Debug menu in safari, which can be done by typing the following into terminal (make sure safari is closed):
% defaults write com.apple.Safari IncludeDebugMenu 1
Then relaunch safari, and from the debug menu you can open a js console.
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Amazing.