D3 zoomable timeline, how to get actual extreme values?

I have a zoomable timeline in d3:

var zoom = d3.behavior.zoom().on("zoom", draw);

With a default domain of 1 year, it will be rendered like this:

20 Jan 2015 ...........2 feb..... 10 feb 2016

When i zoom in or zoom out i would like to get actual viewable limit date. e.g. when i zoom in i have

10 aug 2015 ....30 aug....09 sep 2015

I would catch first and last value of the scale (10 aug and 09 sep) My code:

svg.append("rect")
                .attr("class", "pane")
                .attr("width", width)
                .attr("height", height)
                .call(zoom)
                .on("mouseup", function(){
                     //...here i need to catch 10 aug and 09 sep
                 });

How can I do?

Solution

If you link your zoom to your domains:

var zoom = d3.behavior.zoom()
  .x(x)
  .y(y)
  .on("zoom", zoomed);

Then the x.domain() is auto-magically set after zoom:

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("mouseup", function(d){
    console.log(x.domain());
  });

Example:

<!DOCTYPE html>
<meta charset="utf-8">
<title>Zoom + Pan</title>
<style>

body {
  position: relative;
  width: 960px;
}

svg {
  font: 10px sans-serif;
  shape-rendering: crispEdges;
}

rect {
  fill: #ddd;
}

.axis path,
.axis line {
  fill: none;
  stroke: #fff;
}


</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x = d3.time.scale()
    .domain([new Date(2012, 0, 1), new Date(2013, 0, 1)])
    .range([0, width]);

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()
    .x(x)
    .y(y)
    .on("zoom", zoomed);

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("mouseup", function(d){
      console.log(x.domain());
    })

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);

function zoomed() {
  svg.select(".x.axis").call(xAxis);
  svg.select(".y.axis").call(yAxis);
}

</script>
</body>