25. SVG element tooltip

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
    
		<title>D3: An SVG element tooltip</title>
    
		<script type="text/javascript" src="https://d3js.org/d3.v4.min.js"></script>
		<style type="text/css">

rect:hover {
				fill: orange;
			}

</style>
	</head>
	<body>
		<script type="text/javascript">

var w = 600;
			var h = 250;
			
			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) + ")";
			   })
      
// ---- mouseover to create a svg text to display value on (x,y)   ------------   
			   .on("mouseover", function(d) {

//Get this bar's x/y values for tooltip's (x,y)
					var xPosition = parseFloat(d3.select(this).attr("x")) + xScale.bandwidth() / 2;
					var yPosition = parseFloat(d3.select(this).attr("y")) + 14;

// ---- create a text on svg, not at the rect
					svg.append("text")
					   .attr("id", "tooltip")
					   .attr("x", xPosition)
					   .attr("y", yPosition)
					   .attr("text-anchor", "middle")
					   .attr("font-family", "sans-serif")
					   .attr("font-size", "11px")
					   .attr("font-weight", "bold")
					   .attr("fill", "black")
					   .text(d);

})
      
      
			   .on("mouseout", function() {
			   
					//Remove the tooltip
					d3.select("#tooltip").remove();
					
			   })
      
      
			   .on("click", function() {
			   		sortBars();
			   });

var sortOrder = false;

var sortBars = function() {

// ---- when doing sorting transition, firstly remove tooltip text -----
				d3.select("#tooltip").remove();
        
			   	sortOrder = !sortOrder;

svg.selectAll("rect")
				   .sort(function(a, b) { 
				   		if (sortOrder) {
					   		return d3.ascending(a, b);
				   		} else {
					   		return d3.descending(a, b);
				   		}
				   	})
				   .transition()
				   .delay(function(d, i) {
					   return i * 50;
				   })
				   .duration(1000)
				   .attr("x", function(d, i) {
				   		return xScale(i);
				   });

};

</script>
	</body>
</html>

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