better.js

function f(n){var m=Math,s=m.sqrt(5),g=(1+s)/2,p=m.pow;return m.round((p(g,n)-p(1-g,n))/s);} // accurate version
var m=Math,s=m.sqrt(5),g=(1+s)/2,p=m.pow,f=function(n){return m.round((p(g,n)-p(1-g,n))/s)}; // accurate w/pre-calculating

function f(n){var m=Math,s=m.sqrt(5),g=(1+s)/2,p=m.pow;return((p(g,n)-p(1-g,n))/s);} // inaccurate version
var m=Math,s=m.sqrt(5),g=(1+s)/2,p=m.pow,f=function(n){return((p(g,n)-p(1-g,n))/s)}; // inacurate w/pre-calculating

fib.coffee

# Fibonacci efficient
c=[0,1];f=(i)->[c[i] ?(->c[i]=f(i-1)+f i-2)(),0][+!i]
c=[0,1];f=(i)->c[i] ?(->c[i]=f(i-1)+f i-2)()
c=[0,1];f=(i)->c[i] ?(->c[i]=f(--i)+f --i)()

# Factorial
f=(i)->[(->i*f i-1),->1][+!i]()

fib.js

// Factorial
function f(i){return!i?1:f(i-1)*i}

// Fibonacci short
function b(i){return i<2?i:b(i-1)+b(i-2)}
function b(i){return i<2?i:b(--i)+b(--i)}
 
// Fibonacci efficient
function a(i){return!i?0:(a.c[i]||(a.c[i]=a(i-1)+a(i-2)))}a.c=[,1]