Tutorial D3 2

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    rect {fill: steelblue;}
  </style>
</head>

<body>
  <div id="chart"></div>
  <script>
var myData=[12, 15, 45, 50, 45,56];

var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 100 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var wScale = d3.scaleLinear()
	.range([0, width]);

var colScale = d3.scaleOrdinal(d3.schemeCategory20);
  
var BAR_HEIGHT = 20;

var svg = d3.select("#chart").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 + ")");

function update(myData) {

wScale.domain([0, d3.max(myData)]);
  
	var bars = svg.selectAll(".bars")
  	.data(myData);
  
  //Enter
  var barsEnter = bars.enter()
  	.append("rect")
    .attr("class", "bars")
    .attr("width", 0);
  
  //Exit
  bars.exit()
  	.transition()
    .duration(1000)
    .attr("width", 0)
  	.remove();
 
  //Update
  bars.merge(barsEnter)
  	.attr("x", 0)
    .attr("y", function(d, i ) { return i * (BAR_HEIGHT+1);})
    .attr("height", BAR_HEIGHT)
    .style("fill", function(d,i) { return colScale(i); })
    .transition().duration(1000)
    .attr("width", function(d) { return wScale(d); });

}

update(myData);
    
  </script>
</body>

https://d3js.org/d3.v4.min.js