code: function buildForXStatement(op) {
    return function (node, print) {
      this.keyword("for");
      this.push("(");
      print.plain(node.left);
      this.push(" " + op + " ");
      print.plain(node.right);
      this.push(")");
      print.block(node.body);
    };
  }
docs: Builds ForIn or ForOf statement printers.
  Prints left, right, and body.