How do I update json data in postgres sql in nodejs?

my data structure schema is like

users(
  id serial primary key,
  data json
);

I want to update data key.

So far I have tried something like this:

pg.connect(process.env.DATABASE_URL, function(err, client, done) {
    var queryString = "UPDATE users SET data =" + myNewJsonData + " WHERE  id = " + userIdToEdit + ";";
    client.query(queryString, function(err, result) {
        done();
        if (err) {
            res.send("Failed to update user data ");
            throw err;
        } else {
            res.send("Successfully updated user data!! ");
        }
    });
});

this is not working, I'm getting error invalid input syntax for type json

Can anyone help, Thanks.

via Abhishek