Question

Is it ok to invoke a returned function that is creating a closure like in my code below?

So that when gaining access to the html I do not have to do a Bay.HTML()(); ?

Bay.prototype.HTML = function () {
    var html;
    return function () {
        if (!html) {
            var td = docCreate('td');
            td.setAttribute('id', 'bay' + this.number);
            td.setAttribute('class', 'bay');
            html = td;
        }
        return html;
    }(); <----------HERE
};

Answer 1

I guess you wanted

Bay.prototype.HTML = (function () {
    var html;
    return function () {
        if (!html) {
            var td = docCreate('td');
            td.setAttribute('id', 'bay' + this.number);
            td.setAttribute('class', 'bay');
            html = td;
        }
        return html;
    };
})(); <----------HERE

This assigns the function which is returned from the closure to Bay.prototype.HTML, instead of executing a useless function instantly every time Bay.prototype.HTML is invoked – not really creating a closure.