2012 04 18 changing variables changes arguments

It turns out that changing the value of an argument variable will change its value in the arguments "array":

    > function hello(what) {
    .     what = "world";
    .     return "Hello, " + arguments[0] + "!";
    . }
    > hello("shazow")
    "Hello, world!"

This is documented behaviour (see NOTE 1 in §10.6 Arguments Object of ECMA-262).

I suspect, without evidence, that this allows named argument value lookups to be transformed at compile time into a lookup into the arguments array (so, for example, the what = "world"; would be transformed into arguments[0] = "world"; much like Python's fast locals).

@wolever