Imaging you want to write German words like Straße but you don't have the ß character on your keybord. Those times are over with ß.js. ß.js will automatically turn all ss into ß. You can see the replaced stuff below.

// Include ss.js

var before = 'I live in the Musterstrasse in a town called Gross-Zimmern',
    after = ß(before);

console.log(after);
// => 'I live in the Musterstraße in a town called Groß-Zimmern'.

For speed and performance there's also a minified version of the script called ß.min.js. There's a working example over at CodePen