How to update collection in init.js using Mongo script?

I have the following collection

users

{
    "_id" : ObjectId("..."),
    "username" : "admin",

    "permissions" : {
        "keycloakId" : "...",
        "roles" : [ 
            "admin"
        ]
    },
}

I need to update roles field. I want to assign new role to every user. How can I iterate over collection using mongo script which I am gonna put to docker-entrypoint-initdb.d / init.js?

Here is my code

db.getCollection('users').find({}).forEach(
  function (elem) {
    elem.update({
      _id: elem._id
      }, {
        $set: {
          permissions.roles: ['newRole']
        }
      }
    );
  }
)

I got this error:

2022-12-01T09:51:17.394+0000 E  QUERY    [js] uncaught exception: SyntaxError: missing : after property id :
@(shell):9:30
2022-12-01T09:51:17.395+0000 E  QUERY    [js] uncaught exception: SyntaxError: expected expression, got '}' :