Programmatically and smoothly zoom to the centre.

Programmatically and smoothly zoom to the centre. Adapated from /mbostock/3680999

Zoom buttons will zoom to the centre of the vis smoothly over 350ms.

<!DOCTYPE html>
<meta charset="utf-8">
<title>Zoom + Pan</title>
<script src="https://d3js.org/d3.v3.min.js"></script>
<style>

.overlay {
  fill: none;
  pointer-events: all;
}
button {
  padding: 10px 20px;
}

</style>
<body>
<button id="zoom_in">+</button>
<button id="zoom_out">-</button>
<script>
var width = 960,
    height = 500;

var randomX = d3.random.normal(width / 2, 80),
    randomY = d3.random.normal(height / 2, 80);

var data = d3.range(2000).map(function() {
    return [randomX(), randomY() ];
});

var zoom = d3.behavior.zoom().scaleExtent([1, 8]).on("zoom", zoomed);

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g")
    .call(zoom)
  .append("g");

svg.append("rect")
    .attr("class", "overlay")
    .attr("width", width)
    .attr("height", height);

svg.selectAll("circle")
    .data(data)
  .enter().append("circle")
    .attr("r", 2.5)
    .attr("transform", function(d) { return "translate(" + d + ")"; });

function zoomed() {
    svg.attr("transform",
        "translate(" + zoom.translate() + ")" +
        "scale(" + zoom.scale() + ")"
    );
}

function zoomClick() {
    var clicked = d3.event.target,
        direction = 1,
        factor = 0.2,
        target_zoom = 1,
        center = [width / 2, height / 2],
        extent = zoom.scaleExtent(),
        translate = zoom.translate(),
        translate0 = [],
        l = [],
        view = {x: translate[0], y: translate[1], k: zoom.scale()};

d3.event.preventDefault();
    direction = (this.id === 'zoom_in') ? 1 : -1;
    target_zoom = zoom.scale() * (1 + factor * direction);

if (target_zoom < extent[0] || target_zoom > extent[1]) { return false; }

translate0 = [(center[0] - view.x) / view.k, (center[1] - view.y) / view.k];
    view.k = target_zoom;
    l = [translate0[0] * view.k + view.x, translate0[1] * view.k + view.y];

view.x += center[0] - l[0];
    view.y += center[1] - l[1];

interpolateZoom([view.x, view.y], view.k);
}

d3.selectAll('button').on('click', zoomClick);

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js