Text classifiers (used in forums, for example) have been around for a long time.
Typically this type of text classification and scoring is performed with Bayesian classifiers.
If you do a Google search with keywords:
bayesian classifier ruby
and /or
bayesian classifier javascript
You will find myriad libraries and examples of text classification using Bayesian classifiers.
We have used various Bayesian classifiers for forum post moderation, spam detection, and more over the years; and have implemented custom code to train the classifier when moderators perform mod actions.