I don't know much about how to architect JavaScript applications, but I am struck by how much of this stuff seems to be glued together by strings. For example, from footer.js (https://github.com/box/t3js/blob/master/examples/todo/js/mod...)

    switch(name) {
        case 'todoadded':
        case 'todoremoved':
        case 'todostatuschange':
            this.updateTodoCounts();
        break;

        case 'statechanged':
            this.updateSelectedFilterByUrl(data.url);
            break;
    }

Accidentally wrote 'todostatuschanged' instead of 'todostatuschange' (in keeping with the tense of all the other actions!) and you'll get a silent failure.

Or from isListCompleted() in the list module:

    moduleEl.querySelectorAll('#todo-list li input[type="checkbox"]')

I'm not picking on T3, since all JavaScript frameworks seem to have this problem. There has to be a better way than that!