Add a horizontal line at a specific point in chart.js when hovering - Javascript Chart.js

Javascript examples for Chart.js:Line Chart

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Description

Add a horizontal line at a specific point in chart.js when hovering

Demo Code

ResultView the demo in separate window 

<html>
   <head> 
      <title>chart.js annotations onHover</title> 
      <meta name="viewport" content="width=device-width, initial-scale=1"> 
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.1/Chart.bundle.min.js"></script> 
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/chartjs-plugin-annotation/0.5.7/chartjs-plugin-annotation.min.js"></script> 
      <script type="text/javascript">
    window.onload=function(){/*from   www.j  av  a2 s.co  m*/
var data_set = [{x: 1, y: 12}, {x: 2, y: 3}, {x: 3, y: 2}, {x: 4, y: 1}, {x: 5, y: 8}, {x: 6, y: 8}, {x: 7, y: 2}, {x: 8, y: 2}, {x: 9, y: 3}, {x: 10, y: 5}, {x: 11, y: 11}, {x: 12, y: 1}];
var labels = ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"];
var lines = [], id = 0;
var linesOn = false;
var data = {
  labels: labels,
  datasets: [{
    label: "My First dataset",
    backgroundColor: "rgba(255,99,132,0.2)",
    borderColor: "rgba(255,99,132,1)",
    borderWidth: 2,
    hoverBackgroundColor: "rgba(255,99,132,0.4)",
    hoverBorderColor: "rgba(255,99,132,1)",
    data: data_set,
  }]
};
var option = {
  legend: false,
  title: {
    display: true,
  },
  onHover: function(evt) {
     console.log("onHover", evt.type);
    if (evt.type == 'mousemove' && linesOn == false) {
       linesOn = true;
      myLineChart.options.annotation.annotations = lines;
      myLineChart.update();
    } else if (evt.type == 'mouseout' && linesOn == true) {
       linesOn = false;
       myLineChart.options.annotation.annotations = [];
       myLineChart.update();
    }
    var item = myLineChart.getElementAtEvent(evt);
    if (item.length) {
      console.log(">item", item);
      console.log(">data", item[0]._index, data.datasets[0].data[item[0]._index]);
    }
  },
  onClick: function(evt) {
    var el = myLineChart.getElementAtEvent(evt);
    console.log("onClick", el, evt);
  },
  annotation: {
    drawTime: "afterDraw",
    annotations: lines
  },
  scales: {
    xAxes: [{
      id: 'x-axis',
      type: 'linear',
      position: 'bottom',
      ticks: {
        max: 12,
        min: 1,
        stepSize: 1,
        callback: function(value, index, values) {
          return data.labels[index];
        }
      }
    }],
    yAxes: [{
      id: 'y-axis',
      type: 'linear',
    }],
  }
};
var myLineChart = Chart.Line('myChart', {
  data: data,
  options: option
});
addLine(3.5);
addLine(7);
function addLine(value) {
  id++;
  var ln = {
    id: "line" + id,
    type: "line",
    mode: "horizontal",
    scaleID: "y-axis",
    value: value,
    borderWidth: 2,
    borderColor: "red",
    label: {
      content: "threshold " + id,
      enabled: true,
      position: "right"
    }
  };
  lines.push(ln);
}
    }

      </script> 
   </head> 
   <body> 
      <canvas id="myChart" width="400" height="200"></canvas>  
   </body>
</html>

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