18.add-bar-fromLeft-transition

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
    
		<title>D3: Adding values and elements to a chart</title>
    
		<script type="text/javascript" src="https://d3js.org/d3.v4.min.js"></script>
    
		<style type="text/css">
			/* No style rules here yet */
		</style>
    
	</head>
	<body>
	
		<p>Click on this text to add a new data value to the chart!</p>
			
		<script type="text/javascript">

var w = 600;
			var h = 450;
			
			var dataset = [ 5, 10, 13, 19, 21, 25, 22, 18, 15, 13,
							11, 12, 15, 20, 18, 17, 16, 18, 23, 25 ];
			
			var xScale = d3.scaleBand()
							.domain(d3.range(dataset.length))
							.rangeRound([0, w])
      				.padding(0.05);
      
			var yScale = d3.scaleLinear()
							.domain([0, d3.max(dataset)])
							.range([h, 0]);

var svg = d3.select("body")
						.append("svg")
						.attr("width", w)
						.attr("height", h);

svg.selectAll("rect")
			   .data(dataset)
			   .enter()
			   .append("rect")
			   .attr("x", function(d, i) {
			   		return xScale(i);
			   })
			   .attr("y", function(d) {
			   		return yScale(d);
			   })
			   .attr("width", xScale.bandwidth())
			   .attr("height", function(d) {
			   		return h - yScale(d);
			   })
			   .attr("fill", function(d) {
					return "rgb(0, 0, " + (d * 10) + ")";
			   });
      
			
			svg.selectAll("text")
			   .data(dataset)
			   .enter()
			   .append("text")
			   .text(function(d) {
			   		return d;
			   })
			   .attr("text-anchor", "middle") 
			   .attr("x", function(d, i) {
			   		return xScale(i) + xScale.bandwidth() / 2;
			   })
			   .attr("y", function(d) {
			   		return yScale(d) + 14;
			   })
			   .attr("font-family", "sans-serif")
			   .attr("font-size", "11px")
			   .attr("fill", "white");
      
			
			d3.select("p")
				.on("click", function() {

var maxValue = 25;
					var newNumber = Math.floor(Math.random() * maxValue);	
					dataset.push(newNumber);

// ---- Now, dataset is one element longer -------
// 1. data-input range is 1 element longer
// 2. bandwidth is smaller to fit 1 more bar 
					xScale.domain(d3.range(dataset.length));	
        
					yScale.domain([0, d3.max(dataset)]);

// ---- update dataset is same old dataset
					var bars = svg.selectAll("rect")
						.data(dataset);

bars.enter()	
						.append("rect")		
						.merge(bars)
        
					.transition()			
						.duration(1000)
						.attr("x", function(d, i) {		
							return xScale(i);
						})
						.attr("y", function(d) {			
							return yScale(d);
						})
// ---- this bandwidth is smaller than previous bandwidth-------
						.attr("width", xScale.bandwidth())	
						.attr("height", function(d) {			
							return h - yScale(d);
						})
          	.attr("fill", function(d) {
					return "rgb(0, 0, " + (d * 10) + ")";
			   });

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