This is a JavaScript tool that converts text to use the archaic long S letter ( ſ ) in its spellings.
English, French, German, Spanish, and Italian are supported.
It's a JavaScript version of my original Python code found at py-long-s.
Thank you Andrew West of the TeX Users Group for the documentation found under The Rules for Long S, which was fundamental in writing the conversion functions for English, French, Spanish, and Italian.