The syntax could be a lot cleaner... the Universal Module Definition (UMD) pattern at the top makes it a bit quirky... A lot of people have moved towards using CommonJS (cjs/node-style) exports with tooling such as browserift/webpack and/or babel (for es6 modules) in order to clean up the source syntax.

What you're looking at is a relatively poor example. In es6, that could be ...

    exports default function...

without all the cruft around it, also the module itself could be cleaner. Similar to:

    var cookies = parse();

    export function set({key, value, days=null}) {
      ...
    }

    export function get(key) {
      ...
    }

    export const remove = (key) => set({key, value:null});

    export function parse(values = document && document.cookie || '') {
       ...
    }