D3 Examples - Changing Zoom Domain

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<!DOCTYPE html>
<meta charset="utf-8">
<title>Zoom Behaviour and Timer</title>
<script src="https://d3js.org/d3.v2.min.js?2.10.1"></script>
<style>
​
body {
  font-family: sans-serif;
}
​
.noselect {
  -webkit-touch-callout: none;
  -webkit-user-select: none;
  -khtml-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}
​
svg {
  font: 10px sans-serif;
  shape-rendering: crispEdges;
}
​
rect {
  fill: #ddd;
}
​
rect.zoom {
  stroke: steelblue;
  fill-opacity: 0.5;
}
​
.axis path, .axis line {
  fill: none;
  stroke: #fff;
}
​
</style>
<body>
<script>
​
var margin = {top: 0, right: 12, bottom: 12, left: 36},
    width = 960 - margin.left - margin.right,
    height = 430 - margin.top - margin.bottom;
​
var x0 = d3.scale.linear()
      .domain([-width / 2, width / 2])
      .range([0, width]),
    x = x0.copy();
​
var y = d3.scale.linear()
    .domain([-height / 2, height / 2])
    .range([height, 0]);
​
var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
    .tickSize(-height);
​
var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left")
    .ticks(5)
    .tickSize(-width);
​
var zoom = d3.behavior.zoom()
    .scaleExtent([1, Infinity])
    .x(x)
    .y(y)
    .on("zoom", refresh);
​
var timer = true;
​
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
    .call(zoom)
    .on("mousedown", function() { timer = false; })
    .on("mouseup", function() { timer = true; });
​
svg.append("rect")
    .attr("width", width)
    .attr("height", height);
​
svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis);
​
svg.append("g")
    .attr("class", "y axis")
    .call(yAxis);
​
setInterval(function() {
  if (!timer) return;
  var translate = zoom.translate(),
      scale = zoom.scale(),
      xd = x0.domain(),
      dx = 1;
  // Set a new x-domain: offset by dx.
  xd[0] += dx;
  xd[1] += dx;
  x0.domain(xd)
  // Set the zoom x-domain (this resets the domain at zoom scale=1).
  zoom.x(x.domain(xd));
  // Reset the domain relative to the current zoom offsets.
  x.domain(x0.range().map(function(x) { return (x - translate[0]) / scale; }).map(x0.invert));
  refresh();
}, 1e3);
​
function refresh() {
  svg.select(".x.axis").call(xAxis);
  svg.select(".y.axis").call(yAxis);
}
​
</script>
​
    