Given a string of form field1.field2.field3..., parses it and returns "" if at any point the fields are not defined, or the value of the evaluation if all fields are defined

evalStringObjects.js

  // usage: ifDefined("field1.field2.field3") - do not specify second argument
  ifDefined: function(str_object, prev_eval) {
    var i = str_object.indexOf('.');
    if (i === -1) {
      return true;
    } else {
      var first = str_object.substring(0,i),
          last = str_object.substring(i+1),
          j = last.indexOf('.'),
          second = last;
      if (j !== -1) {
        second = last.substring(0,j);
      }   
      if (typeof prev_eval !== "undefined") {
        first = prev_eval;
      }   
      eval_result = eval(first)[second];
      if (typeof eval_result != "undefined") { 
        var recurse = this.ifDefined(last, eval_result);
        if (recurse === true) {
          return eval_result; //return last eval if returning from base case
        } else {
          return recurse; //otherwise, pass the eval back
        }   
      } else {
        return ""; 
      }   
    }   
  }