21.out-left-add-right-barchart

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
		<title>D3: Adding and removing values from a chart (dynamic labels included)</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 id="add">Add a new data value</p>
		<p id="remove">Remove a data value</p>
			
		<script type="text/javascript">

svg.selectAll("text")
			   .data(dataset, key)
			   .enter()
			   .append("text")
			   .text(function(d) {
			   		return d.value;
			   })
			   .attr("text-anchor", "middle")
			   .attr("x", function(d, i) {
			   		return xScale(i) + xScale.bandwidth() / 2;
			   })
			   .attr("y", function(d) {
			   		return yScale(d.value) + 14;
			   })
			   .attr("font-family", "sans-serif")
			   .attr("font-size", "11px")
			   .attr("fill", "white");

d3.selectAll("p")
				.on("click", function() { 
        
// ---- .on("click", ...) sepcify a dom
        
					var paragraphID = d3.select(this).attr("id");

if (paragraphID == "add") {

var maxValue = 25;
						var newNumber = Math.floor(Math.random() * maxValue);
						var lastKeyValue = dataset[dataset.length - 1].key;
// 						console.log(lastKeyValue);
            
						dataset.push({
							key: lastKeyValue + 1,
							value: newNumber
						});
            
//        // if paragraphID == "remove"
					} else {

dataset.shift();	
					}

xScale.domain(d3.range(dataset.length));
					yScale.domain([0, d3.max(dataset, function(d) { return d.value; })]);

var bars = svg.selectAll("rect")
						.data(dataset, key);

bars.enter()
						.append("rect")
						.attr("x", w)
						.attr("y", function(d) {
							return yScale(d.value);
						})
						.attr("width", xScale.bandwidth())
						.attr("height", function(d) {
							return h - yScale(d.value);
						})
						.attr("fill", function(d) {
							return "rgb(0, 0, " + (d.value * 10) + ")";
						})
        
					.merge(bars)
						.transition()
						.duration(500)
						.attr("x", function(d, i) {
							return xScale(i);
						})
						.attr("y", function(d) {
							return yScale(d.value);
						})
						.attr("width", xScale.bandwidth())
						.attr("height", function(d) {
							return h - yScale(d.value);
						});
        
    
					bars.exit()
						.transition()
						.duration(500)
						.attr("x", -xScale.bandwidth())
						.remove();

var labels = svg.selectAll("text")
						.data(dataset, key);

labels.enter()
						.append("text")
						.text(function(d) {
							return d.value;
						})
						.attr("text-anchor", "middle")
						.attr("x", w)
						.attr("y", function(d) {
							return yScale(d.value) + 14;
						})						
					   .attr("font-family", "sans-serif")
					   .attr("font-size", "11px")
					   .attr("fill", "white")

.merge(labels)
					  .transition()
						.duration(500)
						.attr("x", function(d, i) {
							return xScale(i) + xScale.bandwidth() / 2;
						});

labels.exit()
						.transition()
						.duration(500)
						.attr("x", -xScale.bandwidth())
						.remove();
				}); 
			
		</script>
	</body>
</html>

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