d3 issues with entering elements after pan - d3.js

Question

I use a transform when panning, copied from several examples.
zoom = d3.behavior.zoom()
.x(this.xScale)
.scaleExtent([0.5, 2])
.on("zoom", zoomFunction(this))
.on("zoomend", zoomEndFunction(this));
svg = histogramContainer.append("svg")
.attr('class', 'chart')
.attr('width', width)
.attr('height', height)
.call(zoom)
.append('g')
.attr('transform', 'translate(' + this.margin.left + ' , ' +
(height - this.margin.bottom) + ')');
function zoomFunction(scope) {
return function() {
var that = scope;
that.xDelta = d3.event.translate[0];
that.zoomScale = d3.event.scale;
// some other code removed for simplicity
svg.selectAll(".stackedBar").attr("transform", "translate(" +
that.xDelta + ",0)scale(" +
that.zoomScale + ", 1)");
};
}
The problem is that since new elements enter after the pan then 'old' elements have the transform attribute applied but the new elements don't.
This breaks future panning because the old elements will be transformed from where the pre-zoom xScale drew them while the new elements will be transformed from the zoom-adjusted xScale.
It seems to me that I could redraw the old elements with the zoom-adjusted xScale, though I'm unsure when and how to do that "behind the scenes".
Alternatively I could draw the new elements with the old xScale and apply the same transform on them that the old elements have. This seems messier since elements will come and go and I'll have to keep track of the 'current transform'. My gut tells me "too much state".

Answer 1

Usually if you're attaching a scale to the zoom behaviour, you use the modified scale to redraw the bars using the exact same code as how you position the bars initially, letting the scales do all the work.
I linked to this discussion in my previous answer, so you might have read it by now; if not, it might be a good start for getting your head around the different ways of approaching zooming in d3; it breaks down the each method step-by-step. You're currently using a mix of two approaches (transforms versus scales), and I think that's causing problems keeping track.