javascript - Can I determine if a string is a MongoDB ObjectID?

Question

I am doing MongoDB lookups by converting a string to BSON. Is there a way for me to determine if the string I have is a valid ObjectID for Mongo before doing the conversion?

Here is the coffeescript for my current findByID function. It works great, but I'd like to lookup by a different attribute if I determine the string is not an ID.

db.collection "pages", (err, collection) ->
  collection.findOne
    _id: new BSON.ObjectID(id)
  , (err, item) ->
    if item
      res.send item
    else
      res.send 404

Answer 1

I found that the mongoose ObjectId validator works to validate valid objectIds but I found a few cases where invalid ids were considered valid. (eg: any 12 characters long string)

var ObjectId = require('mongoose').Types.ObjectId;
ObjectId.isValid('microsoft123'); //true
ObjectId.isValid('timtomtamted'); //true
ObjectId.isValid('551137c2f9e1fac808a5f572'); //true

What has been working for me is casting a string to an objectId and then checking that the original string matches the string value of the objectId.

new ObjectId('timtamtomted'); //616273656e6365576f726b73
new ObjectId('537eed02ed345b2e039652d2') //537eed02ed345b2e039652d2

This work because valid ids do not change when casted to an ObjectId but a string that gets a false valid will change when casted to an objectId.