gistfile1.js

function fn1() {}
function fn2() {}
function fn3() {}

function jsListener(fn) {
    var interface = {
        fn1: fn1,
        fn2: fn2,
        fn3: fn3
    }
    var f = interface[fn];
    if (f) {
        var args = [].slice.call(arguments, 1);
        return f.apply(this, args);
    }
}