Plain Code

$.fx.step.togglePair = function( fx ) {
    if ( !fx.togglePair ) {
        fx.togglePair = {};
        $.each( toggleProps, function() {
            var options = {
                complete: fx.options.complete,
                duration: fx.options.duration,
                queue: fx.options.queue
            };
            fx.togglePair[ this ] = new $.fx( fx.elem, options, this );
        });
    }

    var total = 0;
    $.each( fx.togglePair, function( prop, propFx ) {
        propFx.pos = fx.pos;
        propFx.now = propFx.start + (propFx.end - propFx.start) * propFx.pos;
        propFx.now = Math.round( propFx.now );
        total += propFx.now;
        fx.elem.style[ prop ] = propFx.now + propFx.unit;
    });
    // TODO: handle height
};