[TweedHeads]

Full anonimity, thanks to tilly (separated for better understanding):

  builder   = function(x){ return function(n){ return x(x)(n); }}
  factorial = function(f){ return function(n){ return n==0?1:n*f(f)(n-1);} }
  alert(builder(factorial)(8))

One liner, just seed factorial to builder:

  r = (function(x){ return function(n){ return x(x)(n); } } (function(f){ return function(n){ return n==0?1:n*f(f)(n-1);} }))(8);