Within functions, arguments gives access to any parameters passed to the function. But it's a funky object, not a true array. I'm sure the following behavior is documented, but it caught me off-guard. So I thought I'd share.

foo.js

var myFunction = function() {
  if(typeof arguments[0] == 'function') {
    arguments[0](); // throws error: [object Object] is not a function
    // but this works
    var cb = arguments[0];
    cb();
  }
};

myFunction(function() {
  // do something
});