Discouraged usages of `arguments`

Note: The lint check about arguments has been removed in https://github.com/google/closure-compiler/commit/3734b26b1215693d5c46636d91b7a5bb2715f690, but the following patterns are still discouraged.

What's up with the arguments object?

arguments is a variable that is in scope in every function, which more or less acts like an array, but unfortunately is not an array.

There is a lint check that warns about many usages of the arguments variable. If you're iterating over it in a for loop, or accessing specific elements of it, there is no problem. But if you're using Array.prototype.slice to convert it to an Array, or passing it to another function, the linter will give you a warning that looks like:

WARNING - This use of the arguments object is discouraged.
  var args = Array.prototype.slice.call(arguments);
                                        ^

These usages are discouraged. If you pass the Arguments object to another function, it can result in a significant slowdown. See discussion on this bug for more details.

We make an exception for Function.prototype.apply so there is no warning for f.apply(obj, arguments);.