d3 click to center content at position of element or click - d3.js

Question

I have been trying to get the basics of how I make a pannable zoomable, and click to center zoom on element d3 work. This example is what I want to do but I am having trouble translating it outside of the geo context: https://bl.ocks.org/mbostock/2206340
What I have accomplished is the first two parts pan and zoom, see a basic fiddle here https://jsfiddle.net/e9fbn2xp/
How can I accomplish centering the the circle in the center of the viewable window, so it looks like the circle is zoomed to? Note that although this is a fixed position circle I will eventually have dynamic data, so ideally I could reference the circles position dynamically.
Here is my code:
HTML (note that this is React JSX syntax but that should be irrelevant to question)
<div style={{width: 800}}>
<svg style={{border: '1px solid black'}} id="viz" width="800" height="800">
</svg>
</div>
JAVASCRIPT
var svg = d3.select("#viz")
var width = svg.attr("width");
var height = svg.attr("height");
var testLayer = svg.append('g');
var aRect = testLayer.append("rect")
.attr("x", 0)
.attr("y", 0)
.attr("height", 800)
.attr("width", 800)
.attr("fill", 'green');
var aCircle = testLayer.append("circle")
.style("stroke", "gray")
.style("fill", "white")
.attr("r", 40)
.attr("cx", 200)
.attr("cy", 200)
.on("mousedown", zoomToMe);
function zoomToMe(){
console.log("do the zoom")
}
var zoom = d3.zoom()
.scaleExtent([.5, 40])
.translateExtent([[0, 0], [width, height]])
.on("zoom", zoomed);
svg.call(zoom);
function zoomed() {
testLayer.attr("transform", d3.event.transform);
}
svg.on("click", function() {
var coords = d3.mouse(this);
})

Answer 1

I got a working solution and thought I would share the code in case others find it useful. It is a fairly different approach then my original but accomplishes the three goals, pan, mouse zoom, zoom to element. While these are three simple static circles the same concept should work with a dynamic dataset.
fiddle: https://jsfiddle.net/uc7oprx3/5/
HTML
<svg id="viz" width="400" height="400" />
JAVASCRIPT
var zoom = d3.zoom()
.scaleExtent([0.3,2])
.on("zoom", zoomed);
var svg = d3.select("#viz")
var width = svg.attr("width");
var height = svg.attr("height");
var zoomer = svg.append("rect")
.attr("width", width)
.attr("height", height)
.style("fill", "none")
.style("pointer-events", "all")
.call(zoom);
var g = svg.append("g");
var aCircle = g.append("circle")
.style("stroke", "gray")
.style("fill", "white")
.attr("r", 40)
.attr("cx", 200)
.attr("cy", 200)
.on("mousedown", () => centerNode(200, 200));
var bCircle = g.append("circle")
.style("stroke", "gray")
.style("fill", "white")
.attr("r", 40)
.attr("cx", 400)
.attr("cy", 400)
.on("mousedown", () => centerNode(400, 400));
var cCircle = g.append("circle")
.style("stroke", "gray")
.style("fill", "white")
.attr("r", 40)
.attr("cx", 600)
.attr("cy", 600)
.on("mousedown", () => centerNode(600, 600));
function zoomed() {
g.attr("transform", d3.event.transform);
}
function centerNode(xx, yy){
g.transition()
.duration(500)
.attr("transform", "translate(" + (width/2 - xx) + "," + (height/2 - yy) + ")scale(" + 1 + ")")
.on("end", function(){ zoomer.call(zoom.transform, d3.zoomIdentity.translate((width/2 - xx),(height/2 - yy)).scale(1))});
}