Require/define, min.

minreq.js

;(function(where){
   var defined={},required={};
   function define(thing,something){
      defined[thing]=something
   }
   function require(thing){
      required[thing]=required[thing]||defined[thing]()
      return required[thing]
   }
   where.define=define
   where.require=require;
})(this);