I think there's a mistake in the first example, it talks about for-in being bad but the example doesn't actually use for-in. > There is no really good reason t

I think there's a mistake in the first example, it talks about for-in being bad but the example doesn't actually use for-in. > There is no really good reason to predefine the array length. There are good reasons, though they're usually quite 'sneaky', for example: function repeatString(str, howMany) { return new Array(howMany+1).join(str); } > 13. Usage of undefined as a variable... that variables isn’t read-only, and any other code can change its value... why take the risk? There's no good reason to be that paranoid, libraries could also overwrite 'document', 'XMLHttpRequest', 'setTimeout' and a number of other variables that would likely break my code; if any of my libs are so rogue that they overwrite 'undefined' then I've got big problems.