code: private boolean isUndefinedTypeofGuardFor(Node expression, Node reference) {
      if (expression.isNE()) {
        Node undefinedString = expression.getFirstChild();
        Node typeofNode = expression.getLastChild();
        return undefinedString.isString()
            && undefinedString.getString().equals("undefined")
            && typeofNode.isTypeOf()
            && typeofNode.getFirstChild().isEquivalentTo(reference);
      } else {
        return false;
      }
    }
docs: Is the expression of the form {@code 'undefined' != typeof Ref}?
  
  @param expression
  @param reference Ref node must be equivalent to this node