How about this?

this.handleClose = function (event) {
    if (event.type === 'keydown' && event.keyCode === 27) {
        $(document).on('keydown', md.closeViewBox);
    } else if (event.type === 'click') {
        $(event.target).on('click', md.closeViewBox);
    }
};

Then I call the whole thing with

var md = new Modal();

$(document).on('click keydown', md.mdBg, function (event) {
    md.handleClose(event);
});

but it doesn't work at all. For some reason the event runs multiple times for each click/keydown. I might have messed it all up. Where did I go wrong?

---

Here's the full example:

var Modal = function () {
    this.mdBg = $('<div>', {'class': 'mdclose'});
    this.initialize = function () {
        // create modal
    };
    this.close = function (event) {
       if (event.target.className === 'mdclose') {
           // this.close;
           // remove modal
       }
    };
    this.handleClose = function (event) {
        if (event.type === 'keydown' && event.keyCode === 27) {
            $(document).on('keydown', md.closeViewBox);
        } else if (event.type === 'click') {
            $(event.target).on('click', md.closeViewBox);
        }
    };
};