var d = (function() {
    var funcs = [];

    function fire() {
        for (var i=0; i<funcs.length; ++i) {
          funcs[i].call();
        }
    }

    function register(newfunc) {
        funcs.push(newfunc);
    }

    return {
        fire: fire,
        register: register
    };
})();

function A() {

    // do stuff to update the INPUT

    d.fire();
}

d.register(B);