App switching and Clock faces

You could remove one layer of function nesting by making each face a module.

Each face would then follow the format

exports.getFace = function (){
    function onSecond(){
       //draw digits, hands etc
    }
    function drawAll(){
       //draw background + initial state of digits, hands etc
    }
    return {init:drawAll, tick:onSecond};
};

And to load them you'd do something along the lines of

let FACES = require("Storage").list(/\.face\.js$/).map(require);