How does dafont and other font selection sites let you preview trutype fonts?

I would like to integrate a feature into a form on a site I am working on much like fonts.com andill dafont.com and I have looked everywhere using every search term imaginable trying to figure out where to even begin. NOTHING. Here is what I'd like:

User chooses font by name in a drop down list. They can then put there custom text in a form field which will preview in its true type form so they can see what their font will look like.

Basically I want to copy how the font choosing sites allow u to pick your font.. preview it and in my case submit the font choice with the form along with other form data.

Can someone at least point me in the right direction. I am stumped. I think i am overthinking this but its a feature a client is desperate for. Any help would be deeply appreciated and I thank you in advance.