src/language-js/printer-estree-json.js/clean
function clean(node, newNode /*, parent*/) {
  delete newNode.start;
  delete newNode.end;
  delete newNode.extra;
  delete newNode.loc;
  delete newNode.comments;
  delete newNode.errors;

  if (node.type === "Identifier") {
    return { type: "StringLiteral", value: node.name };
  }
  if (node.type === "UnaryExpression" && node.operator === "+") {
    return newNode.argument;
  }
}