Since you mention JavaScript, this is what Douglas Crockford has to say on the topic:
Avoid lines longer than 80 characters. When a statement will not fit on a single line, it may be necessary to break it. Place the break after an operator, ideally after a comma. A break after an operator decreases the likelihood that a copy-paste error will be masked by semicolon insertion. The next line should be indented 8 spaces.
From: Code Conventions for the JavaScript Programming Language
