Your Browser's Result:

-

Browser Results:

Firefox 
form is not callable
Opera 9 
typeof f  "object"
f('0')    [object HTMLFormElement]
f('a')    [object HTMLFormElement]
f('d')    [object HTMLFormElement]
IE6, IE7, IE8 
typeof f  "object"
f('0')    [object]
f('a')    [object]
f('d')    [object]
Safari 
typeof f  "function"
f('0')    [object HTMLFormElement]
f('a')    [object HTMLFormElement]
f('d')    [object HTMLFormElement]