jsonp in google apps scripting

jsonp.gs

/* 
  Suppose there is some endpoint that returns a jsonp to you, as in Google Visualization API
  It gives you a text response that looks like this:
    "some.namespace.nameOfFunction({obj:'blah'})"
  We want the object inside that function call.
  In a google app scripting context, we have no choice but to evaluate it the old-fashioned way, using "evil" eval(). 
  
  This solution builds a variable that resolves the namespace some.namespace.blah.blah and which ultimately becomes 
    a function that returns the passed parameter.
    We build the variable with raw text, then eval it, giving the local context the ability to resolve the namespace and
    call the function.
    Then we are able to eval("some.namespace.nameOfFunction(...)") and get the original object
*/

jsonp = function (callbackPath, responseText) {
  var path, split, first, last, middle, buildEval, arr=[];
  split = callbackPath.split('.');
  first = split[0];
  middle = split.slice(1, split.length);
  last = 'function (obj) { return obj; }';  // anonymous function that is always the value of the resolved path

  arr[middle.length-1] = '';  // set up to do arr.join('}') which gives us our final braces
  buildEval = 'var ' + first + ' = ' + middle.reduce(
    function (acc, item, index) {
      acc += '{"' + item + '": ';
      return acc;
    },
  '') + last + (middle.length > 0 ? '}' : '') + arr.join('}') + ';';        

  eval(buildEval);

  return eval(responseText);
};