Comments just for the commenter, with Echochamber.js:

When a user submits a comment, echochamber.js will save the comment to the user’s LocalStorage, so when they return to the page, they can be confident that their voice is being heard, and feel engaged with your very engaging content. It does not make any HTTP requests. Since LocalStorage is only local, you and your database need not be burdened with other people’s opinions.

Or in layman terms: The comments only live in the commenter’s browser, thus that’s the only place it exists.