var pi ={}

​

function setWDef () {

   var args = [].slice.call(arguments);

   var obj = args.shift();

   var _obj = obj;

   var val = args.pop();

   if(typeof obj !== "object") throw new TypeError ("Expected first argument to be of type object");

  for (var i = 0,j = args.length - 1;i<j;i++) {

    var curr = args[i];

    if(!_obj[curr]) _obj[curr] = {};

        _obj = _obj[curr];

  }

  _obj[args.pop()] = val;

  return obj;

}

console.log (setWDef(pi,"0","*","a*",1))