exc.js

// exception.js

var ObjectId = require('mongojs').ObjectId
  , id = '000000000000000000000000';

for (var i = 0; i < 1000000; i++) {
  try {
    var _id = ObjectId(id);
  } catch (e) { 
    //  
  }
}

// noexception.js

var ObjectId = require('mongojs').ObjectId
  , id = '000000000000000000000000';

for (var i = 0; i < 1000000; i++) {
  if (/^[0-9a-f]{24}$/.test(id)) {
    var _id = ObjectId(id);
  }
}