Gauge D3.js display value at the top of the needle

Question

I'm kinda new to D3.js, and I managed to create a gauge with what I found on the Internet. But I couldn't find any gauge showing the current value at the top of the needle. Something like this : what I want

Obviously I'd like the value to follow the needle. I tried to add "text" attribute to the needle itself, but it didn't work.

Here's a codepen link : http://codepen.io/kazu_codepen/pen/wGmGjv?editors=1010

Here's my js code :

// data which need to be fetched

var name = "azerty";

var value = 17;


var gaugeMaxValue = 100; 

// data to calculate 
var percentValue = value / gaugeMaxValue; 

////////////////////////

var needleClient;



(function(){

var barWidth, chart, chartInset, degToRad, repaintGauge,
    height, margin, numSections, padRad, percToDeg, percToRad, 
    percent, radius, sectionIndx, svg, totalPercent, width;



  percent = percentValue;

  numSections = 1;
  sectionPerc = 1 / numSections / 2;
  padRad = 0.025;
  chartInset = 10;

  // Orientation of gauge:
  totalPercent = .75;

  el = d3.select('.chart-gauge');

  margin = {
    top: 20,
    right: 20,
    bottom: 30,
    left: 20
  };

  width = el[0][0].offsetWidth - margin.left - margin.right;
  height = width;
  radius = Math.min(width, height) / 2;
  barWidth = 40 * width / 300;



  //Utility methods 

  percToDeg = function(perc) {
    return perc * 360;
  };

  percToRad = function(perc) {
    return degToRad(percToDeg(perc));
  };

  degToRad = function(deg) {
    return deg * Math.PI / 180;
  };

  // Create SVG element
  svg = el.append('svg').attr('width', width + margin.left + margin.right).attr('height', height + margin.top + margin.bottom);

  // Add layer for the panel
  chart = svg.append('g').attr('transform', "translate(" + ((width + margin.left) / 2) + ", " + ((height + margin.top) / 2) + ")");


  chart.append('path').attr('class', "arc chart-first");
  chart.append('path').attr('class', "arc chart-second");
  chart.append('path').attr('class', "arc chart-third");


  arc3 = d3.svg.arc().outerRadius(radius - chartInset).innerRadius(radius - chartInset - barWidth)
  arc2 = d3.svg.arc().outerRadius(radius - chartInset).innerRadius(radius - chartInset - barWidth)
  arc1 = d3.svg.arc().outerRadius(radius - chartInset).innerRadius(radius - chartInset - barWidth)

  repaintGauge = function () 
  {
    perc = 0.5;
    var next_start = totalPercent;
    arcStartRad = percToRad(next_start);
    arcEndRad = arcStartRad + percToRad(perc / 3);
    next_start += perc / 3;


    arc1.startAngle(arcStartRad).endAngle(arcEndRad);

    arcStartRad = percToRad(next_start);
    arcEndRad = arcStartRad + percToRad(perc / 3);
    next_start += perc / 3;

    arc2.startAngle(arcStartRad + padRad).endAngle(arcEndRad);

    arcStartRad = percToRad(next_start);
    arcEndRad = arcStartRad + percToRad(perc / 3);

    arc3.startAngle(arcStartRad + padRad).endAngle(arcEndRad);

    chart.select(".chart-first").attr('d', arc1);
    chart.select(".chart-second").attr('d', arc2);
    chart.select(".chart-third").attr('d', arc3);


  }
/////////

    var dataset = [{metric:name, value: value}]

    var texts = svg.selectAll("text")
                .data(dataset)
                .enter();

    texts.append("text")
         .text(function(){
              return dataset[0].metric;
         })
         .attr('id', "Name")
         .attr('transform', "translate(" + ((width + margin.left) / 6) + ", " + ((height + margin.top) / 1.5) + ")")
         .attr("font-size",25)
         .style("fill", "#000000");


    texts.append("text")
         .text(function(){
            return dataset[0].value;
         })
         .attr('id', "Value")
         .attr('transform', "translate(" + ((width + margin.left) / 1.4) + ", " + ((height + margin.top) / 1.5) + ")")
         .attr("font-size",25)
         .style("fill", "#000000");




    texts.append("text")
        .text(function(){
            return 0;
        })
        .attr('id', 'scale0')
        .attr('transform', "translate(" + ((width + margin.left) / 100 ) + ", " + ((height + margin.top) / 2) + ")")
        .attr("font-size", 15)
        .style("fill", "#000000");

    texts.append("text")
        .text(function(){
            return gaugeMaxValue/2;
        })
        .attr('id', 'scale10')
        .attr('transform', "translate(" + ((width + margin.left) / 2.15 ) + ", " + ((height + margin.top) / 30) + ")")
        .attr("font-size", 15)
        .style("fill", "#000000");


    texts.append("text")
        .text(function(){
            return gaugeMaxValue;
        })
        .attr('id', 'scale20')
        .attr('transform', "translate(" + ((width + margin.left) / 1.03 ) + ", " + ((height + margin.top) / 2) + ")")
        .attr("font-size", 15)
        .style("fill", "#000000");

  var Needle = (function() {

    //Helper function that returns the `d` value for moving the needle
    var recalcPointerPos = function(perc) {
      var centerX, centerY, leftX, leftY, rightX, rightY, thetaRad, topX, topY;
      thetaRad = percToRad(perc / 2);
      centerX = 0;
      centerY = 0;
      topX = centerX - this.len * Math.cos(thetaRad);
      topY = centerY - this.len * Math.sin(thetaRad);
      leftX = centerX - this.radius * Math.cos(thetaRad - Math.PI / 2);
      leftY = centerY - this.radius * Math.sin(thetaRad - Math.PI / 2);
      rightX = centerX - this.radius * Math.cos(thetaRad + Math.PI / 2);
      rightY = centerY - this.radius * Math.sin(thetaRad + Math.PI / 2);
      return "M " + leftX + " " + leftY + " L " + topX + " " + topY + " L " + rightX + " " + rightY;
    };

    function Needle(el) {
      this.el = el;
      this.len = width / 2.5;
      this.radius = this.len / 8;
    }

    Needle.prototype.render = function() {
      this.el.append('circle').attr('class', 'needle-center').attr('cx', 0).attr('cy', 0).attr('r', this.radius);

        ///////
        /**
        *
        * I tried to add text here
        *
        */
        ///////

      return this.el.append('path').attr('class', 'needle').attr('id', 'client-needle').attr('d', recalcPointerPos.call(this, 0));


    };

    Needle.prototype.moveTo = function(perc) {
      var self,
          oldValue = this.perc || 0;

      this.perc = perc;
      self = this;

      // Reset pointer position
      this.el.transition().delay(100).ease('quad').duration(200).select('.needle').tween('reset-progress', function() {
        return function(percentOfPercent) {
          var progress = (1 - percentOfPercent) * oldValue;

          repaintGauge(progress);
          return d3.select(this).attr('d', recalcPointerPos.call(self, progress));
        };
      });

      this.el.transition().delay(300).ease('bounce').duration(1500).select('.needle').tween('progress', function() {
        return function(percentOfPercent) {
          var progress = percentOfPercent * perc;

          repaintGauge(progress);
          return d3.select(this).attr('d', recalcPointerPos.call(self, progress));
        };
      });

    };


    return Needle;

  })();



  needle = new Needle(chart);
  needle.render();
  needle.moveTo(percent);   

})();

And here's my html code :

<!DOCTYPE html>
<html>
    <head>
        <script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>
        <style type="text/css" src="gauge.css">
            .chart-gauge
            {
              width: 400px;
              margin: 100px auto  
             } 
            .chart-first
            {
                fill: #9FBD35;
            }
            .chart-second
            {
                fill: #F2BA3A;
            }
            .chart-third
            {
                fill: #FB3033;
            }

            .needle, .needle-center
            {
                fill: #000000;
            }
            .text {
                color: "#112864";
                font-size: 16px;
            }


            svg {
              font: 10px sans-serif;
            }


        </style>

    </head>
    <body>


        <div class="chart-gauge"></div>



        <script type="text/javascript" src="./gaugeClient.js"></script>
        <script type="text/javascript" src="./labels.js"></script>
        <script src="https://d3js.org/d3.v3.min.js" charset="utf-8"></script>
    </body>

</html>

If anyone could help, I've spent few days trying unsuccessfully. Thanks.

Answer 1

Here's an updated codepen

Changes made:

1) As part of initialization, create element valueText

valueText = chart.append("text")
                .attr('id', "Value")
                .attr("font-size",16)
                .attr("text-anchor","middle")
                .attr("dy",".5em")
                .style("fill", '#000000');

2) Also at initialization, create formatValue, to format percent

formatValue = d3.format('1%');

3) At each frame of the transition, compute the position of the text. It adds an offset of 45 units to self.len (the needle's length) to move the text outwards.

var thetaRad = percToRad(progress / 2);
var textX = - (self.len + 45) * Math.cos(thetaRad);
var textY = - (self.len + 45) * Math.sin(thetaRad);

4) Translate valueText based on the computed position and update its text from current progress

valueText.text(formatValue(progress))
  .attr('transform', "translate("+textX+","+textY+")")