This code will result in 9 "E11000 duplicate key error index" errors

mongojs-duplicate-key-test.js

var dbUri = '...';
var db = require('mongojs').connect(dbUri, ['testing']); 

var data = { foo: 1 };
for (var n = 0; n < 10; n++) {
  db.testing.insert(data, function (err, res) {
    if (err) console.log(err.message);
  });
}

The issue seems to be that mongojs adds an _id attribute to the data object, which is then reused after the first insert