Simple bar chart transition

<!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; }
    svg{
      width: 960px;
      height: 400px;
    }
  </style>
</head>

<body>
  <svg></svg>
  <p>Select new value set</p>
  <select id="changeBars">
  <option value="0">First Set<option>
  <option value="1">Second Set<option>
  <option value="2">Third Set<option>
  </select>
  <script>
    const dataValues = [[20, 45, 150, 220], [90, 100, 230, 30, 190], [50, 150, 200]];
		const trans = d3.transition().duration(1000);
    const colors = d3.scaleOrdinal(d3.schemeCategory10);
    const height = 300;
    const rectWidth = 100;
    const svg = d3.select('svg');
    
    function updateBars(data){
      var bars = svg.selectAll('rect')
      	.data(data, d => d);
      
      //exit
      bars.exit().transition(trans)
      	.attr('y', height)
      	.attr('height', 0)
      	.remove();
      
      //enter
      const enter = bars.enter().append('rect')
      	.attr('width', rectWidth)
      	.attr('stroke', '#000')
      	.attr('y', height);
      
      //enter and update
      bars = enter.merge(bars)
      	.attr('x', (d, i) => i * rectWidth)
      	.attr('fill', d => colors(d))
      	.transition(trans)
      	.attr('y', d => height - d)
      	.attr('height', d => d);
    };
    updateBars(dataValues[0]);
    document.getElementById("changeBars").addEventListener('change', (event) => {
      updateBars(dataValues[event.target.value]);
    });
  </script>
</body>

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