namespaces - javascript: prototyping with multiple objects -

sorry if answered somewhere (it is), i'm not quite sure how ask properly, failed @ searching :(

basically want this:

(a||b).prototype.c = function () {   // } 

basically , b objects. 1 or other exist, not both. don't know exist, need add method whichever 1 does.

now, know this:

if (typeof(a) == 'object') {   a.prototype.c = c; } else if (typeof(b) == 'object') {   b.prototype.c = c; }   function c () {   // } 

but has problem of c having own namespace on global level, , don't want that. not want c have it's own namespace on global level @ point in time.

soo...obviously first bit of code above doesn't work. how go this? or not possible? please feel free close , point me in right direction if has been answered before...

i think solve problem:

(function() {   var f = function() {     //prototype function   };   if(a)     a.prototype.f = f;   if(b)     b.prototype.f = f; })();