Place Text in Chart-Canvas Area in ChartJS

Question

I created two x,y arrays and then performed two chart using these. I want to write some texts in only Chart red one. And I want to use (x,y) coordinates to determine text region. I try to Chartjs Global plugin but it causes to writing text all charts. I demand texting only one chart. I could not succeed in Chartjs mono Plugin in Script. Please Help Me.

Here is my code:

<!DOCTYPE html>
<link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css">

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    <div class="w3-row">
        <div class="w3-col s3"><p></p></div>
        <div class="w3-col s6" align="center"><canvas id="myChart" height="120"></canvas></div>
        <div class="w3-col s3"><p></p></div>
    </div>
    <div class="w3-row">
        <div class="w3-col s3"><p></p></div>
        <div class="w3-col s6" align="center"><canvas id="myTau" height="120"></canvas></div>
        <div class="w3-col s3"><p></p></div>
    </div>
</body>
</html>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.min.js"></script>
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
<script type="text/javascript">
    var xCoord = new Array(1997, 2003, 2005, 2009, 2014, 2018, 2019);
    var yCoord = new Array(1, 3, 5, 3, 6, 10, 9);
    var c = [];
    for (var i = 0; i < xCoord.length; i++) {
        var obj = { x: xCoord[i], y: yCoord[i] };
        c.push(obj);
    }
        var ctx = document.getElementById('myChart').getContext('2d');
        var myChart = new Chart(ctx, {
            type: 'line',
            data: {
                datasets: [{
                    label: 'None',
                    data: c,
                    borderWidth: 1,
                    borderColor: "#3e95cd",
                    fill: false,
                    cubicInterpolationMode: 'monotone'
                }
                ]
            },
            options: {
                title: {
                    display: true,
                    text: 'My Chart'
                },
                tooltips: {
                    mode: 'nearest',
                    intersect: true
                },
                scales: {
                    xAxes: [{
                        type: 'linear',
                        position: 'bottom',
                        scaleLabel: {
                            display: true,
                            labelString: 'Year Assembly',
                            fontSize: 14
                                    }
                    }],
                    yAxes: [{
                        scaleLabel: {
                            display: true,
                            labelString: 'Aquifer Values',
                            fontSize: 15
                                    }
                    }]
                }
            }
        });
</script>

<script type="text/javascript">
    var xCoord = new Array(1997, 2003, 2005, 2009, 2014, 2018, 2019);
    var yCoord = new Array(41, 31, 11, 31, 88, 101, 91);
    var c = [];
    for (var i = 0; i < xCoord.length; i++) {
        var obj = { x: xCoord[i], y: yCoord[i] };
        c.push(obj);
    }
    var ctx = document.getElementById('myTau').getContext('2d');
    var myTau = new Chart(ctx, {
        type: 'line',
        data: {
            datasets: [{
                label: 'None',
                data: c,
                borderWidth: 1,
                borderColor: "#ef1414",
                fill: false,
                cubicInterpolationMode: 'monotone'
            }
            ]
        },
        options: {
            title: {
                display: true,
                text: 'My Chart 2'
            },
            tooltips: {
                mode: 'nearest',
                intersect: true
            },
            scales: {
                xAxes: [{
                    type: 'linear',
                    position: 'bottom',
                    scaleLabel: {
                        display: true,
                        labelString: 'Year Assembly',
                        fontSize: 14
                    }
                }],
                yAxes: [{
                    scaleLabel: {
                        display: true,
                        labelString: 'Aquifer Values Corresponding',
                        fontSize: 15
                    }
                }]
            }
        }
    });
</script>

UPDATE:

Here is another problem:

Is there any way to assign text position via chartjs coordinate system, in stead of "width., height."?

For instance, according to xCoord & yCoord arrays, is it possible to set the position of ctx.fillText x,y coordinates:

In stead of ctx.fillText("s(A)", width * .28, height * .70); can be like this : ctx.fillText("s(A)", 2005, 3); (2015,9) is belong to chartjs coordinate system.

My Aim: s(A) can be seen on chartjs area at the point of (2005,3) s(A) can be seen on chartjs area at the point of (2015,9)

My Coordinate Problem Picture

Here is Last Problem Code:

<!DOCTYPE html>
<link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css">

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    <div class="w3-row">
        <div class="w3-col s3"><p></p></div>
        <div class="w3-col s6" align="center"><canvas id="myChart" height="120"></canvas></div>
        <div class="w3-col s3"><p></p></div>
    </div>
    <div class="w3-row">
        <div class="w3-col s3"><p></p></div>
        <div class="w3-col s6" align="center"><canvas id="myTau" height="120"></canvas></div>
        <div class="w3-col s3"><p></p></div>
    </div>
</body>
</html>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.min.js"></script>
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
<script type="text/javascript">
    var plugin = {
        beforeDraw: function (chart) {
            var width = chart.chart.width,
                height = chart.chart.height,
                ctx = chart.chart.ctx;
            ctx.restore();
            ctx.font = "1em sans-serif";
            ctx.textAlign = "center";
            ctx.textBaseline = "middle";
            ctx.fillText("s(A)", width * .28, height * .70);
            ctx.fillText("s(B)", width * .75, height * .55);
            //These section were set according to canvas width and height
            //I want to set coordinates chartjs coordinates like in data {x:1993,y:70}
             // Doesnt Work Like This: ctx.fillText("s(A)", 2005, 2);
             //Doesnt Work Like This: ctx.fillText("s(B)", 2015, 9);
            ctx.save();
        }
    };
    Chart.plugins.register(plugin);

    var xCoord = new Array(1997, 2003, 2005, 2009, 2014, 2018, 2019);
    var yCoord = new Array(1, 3, 5, 3, 6, 10, 9);
    var c = [];
    for (var i = 0; i < xCoord.length; i++) {
        var obj = { x: xCoord[i], y: yCoord[i] };
        c.push(obj);
    }
        var ctx = document.getElementById('myChart').getContext('2d');
        var myChart = new Chart(ctx, {
            type: 'line',
            data: {
                datasets: [{
                    label: 'None',
                    data: c,
                    borderWidth: 1,
                    borderColor: "#3e95cd",
                    fill: false,
                    cubicInterpolationMode: 'monotone'
                }
                ]
            },
            options: {
                plugins: [plugin],
                title: {
                    display: true,
                    text: 'My Chart'
                },
                tooltips: {
                    mode: 'nearest',
                    intersect: true
                },
                scales: {
                    xAxes: [{
                        type: 'linear',
                        position: 'bottom',
                        scaleLabel: {
                            display: true,
                            labelString: 'Year Assembly',
                            fontSize: 14
                                    }
                    }],
                    yAxes: [{
                        scaleLabel: {
                            display: true,
                            labelString: 'Aquifer Values',
                            fontSize: 15
                                    }
                    }]
                }
            }
        });
</script>

Francisco Soares · Accepted Answer · 2019-05-04T21:07:21.410

An working example:

var plugin = {
  id: 'plugin',
  beforeDraw: function(chart) {

    var width = chart.chart.width,
      height = chart.chart.height,
      ctx = chart.chart.ctx,
      xScale = chart.scales['x-axis-0'],
      yScale = chart.scales['y-axis-0'];

    ctx.restore();
    ctx.font = "1em sans-serif";
    ctx.textAlign = "center";
    ctx.textBaseline = "middle";
    // ctx.fillText("s(A)", width * .28, height * .70);
    ctx.fillText(
      "s(A)",
      xScale.getPixelForValue('2005'),
      yScale.getPixelForValue(3)
    );
    ctx.fillText(
      "s(B)",
      xScale.getPixelForValue('2015'),
      yScale.getPixelForValue(9)
    );
    ctx.save();
  }
};

var xCoord = new Array(1997, 2003, 2005, 2009, 2014, 2018, 2019);
var yCoord = new Array(1, 3, 5, 3, 6, 10, 9);
var c = [];
for (var i = 0; i < xCoord.length; i++) {
  var obj = {
    x: xCoord[i],
    y: yCoord[i]
  };
  c.push(obj);
}
var ctx = document.getElementById('myTau').getContext('2d');
var myTau = new Chart(ctx, {
  type: 'line',
  data: {
    datasets: [{
      label: 'None',
      data: c,
      borderWidth: 1,
      borderColor: "#ef1414",
      fill: false,
      cubicInterpolationMode: 'monotone'
    }]
  },
  plugins: [plugin],
  options: {
    title: {
      display: true,
      text: 'My Chart 2'
    },
    tooltips: {
      mode: 'nearest',
      intersect: true
    },
    scales: {
      xAxes: [{
        type: 'linear',
        position: 'bottom',
        scaleLabel: {
          display: true,
          labelString: 'Year Assembly',
          fontSize: 14
        }
      }],
      yAxes: [{
        scaleLabel: {
          display: true,
          labelString: 'Aquifer Values Corresponding',
          fontSize: 15
        }
      }]
    }
  }
});
var ctx = document.getElementById('myTax').getContext('2d');
var myTau = new Chart(ctx, {
  type: 'line',
  data: {
    datasets: [{
      label: 'None',
      data: c,
      borderWidth: 1,
      borderColor: "#ef1414",
      fill: false,
      cubicInterpolationMode: 'monotone'
    }]
  },
  options: {
    title: {
      display: true,
      text: 'My Chart 2'
    },
    tooltips: {
      mode: 'nearest',
      intersect: true
    },
    scales: {
      xAxes: [{
        type: 'linear',
        position: 'bottom',
        scaleLabel: {
          display: true,
          labelString: 'Year Assembly',
          fontSize: 14
        }
      }],
      yAxes: [{
        scaleLabel: {
          display: true,
          labelString: 'Aquifer Values Corresponding',
          fontSize: 15
        }
      }]
    }
  }
});

<canvas id="myTau" height="120"></canvas>
<canvas id="myTax" height="120"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.8.0/Chart.bundle.min.js"></script>
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>

Create and register a new plugin that draw the text, then call it only on the second chart, you can pass data as well (like an array of labels and the locations of each for example).

Update: (register plugins)

If you register a plugin globally then, you will have to disable the plugin in each chart here you don't want it to run.

options: {
    plugins: {
        plugin: false
    }
}

- or -

If you don't register the plugin globally, in each chart that you need to add the labels add the following:

{
    plugins: [plugin]
}

Note: In the second snippet of code plugin is not nested under options. Seen here.

Update: (display text using x,y datasets)

In order to use a x,y value you need to identify the axes you what the value from using its id, the defaults are x-axis-0 and y-axis-0, that increments if you add more axes. Or use a custom axis id.

After that, within the chart instance there is a scale object that represents the axis and using chart.scales['x-axis-0'] you can access a function called getPixelForValue which will convert the giving value from that axis to its pixel location.

When I attemped, this code is well done but in this problem, all charts is written. — drakislow, May 02 '19 at 12:30
@drakislow, I have updated my answer, please view the example again, and let me know the results. — Francisco Soares, May 02 '19 at 13:15
Is there any way to manage text position via chartjs coordinate system, in stead of width., height.? @francisco-soares — drakislow, May 03 '19 at 04:49
@drakislow I don't think so, but please explain what exactly you want to achieve, maybe is possible to calculate the position in other way. — Francisco Soares, May 03 '19 at 09:45
@drakislow there is an way to get the pixel value from an axis value, take a look at the example again. — Francisco Soares, May 04 '19 at 21:08
It's working on type of Line. If there is a scatter chart, can not work these codes. Is there any way to achieve with scatter chart? For Example: https://codepen.io/anon/pen/bypjRv — drakislow, May 10 '19 at 16:34
@drakislow when using the scatter type the default id's start with `1`, so you have to change `x-axis-0` to `x-axis-1` and the same to the `y` axis. — Francisco Soares, May 10 '19 at 17:13

score 0 · Answer 2 · answered May 02 '19 at 12:26

<!DOCTYPE html>
<link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css">

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    <div class="w3-row">
        <div class="w3-col s3"><p></p></div>
        <div class="w3-col s6" align="center"><canvas id="myChart" height="120"></canvas></div>
        <div class="w3-col s3"><p></p></div>
    </div>
    <div class="w3-row">
        <div class="w3-col s3"><p></p></div>
        <div class="w3-col s6" align="center"><canvas id="myTau" height="120"></canvas></div>
        <div class="w3-col s3"><p></p></div>
    </div>
</body>
</html>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.min.js"></script>
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
<script type="text/javascript">
    var plugin = {
        beforeDraw: function (chart) {
            var width = chart.chart.width,
                height = chart.chart.height,
                ctx = chart.chart.ctx;
            ctx.restore();
            ctx.font = "1em sans-serif";
            ctx.textAlign = "center";
            ctx.textBaseline = "middle";
            ctx.fillText("s(A)", width * .28, height * .70);
            ctx.fillText("s(B)", width * .75, height * .55);
            ctx.save();
        }
    };
    Chart.plugins.register(plugin);

    var xCoord = new Array(1997, 2003, 2005, 2009, 2014, 2018, 2019);
    var yCoord = new Array(1, 3, 5, 3, 6, 10, 9);
    var c = [];
    for (var i = 0; i < xCoord.length; i++) {
        var obj = { x: xCoord[i], y: yCoord[i] };
        c.push(obj);
    }
        var ctx = document.getElementById('myChart').getContext('2d');
        var myChart = new Chart(ctx, {
            type: 'line',
            data: {
                datasets: [{
                    label: 'None',
                    data: c,
                    borderWidth: 1,
                    borderColor: "#3e95cd",
                    fill: false,
                    cubicInterpolationMode: 'monotone'
                }
                ]
            },
            options: {
                plugins: [plugin],
                title: {
                    display: true,
                    text: 'My Chart'
                },
                tooltips: {
                    mode: 'nearest',
                    intersect: true
                },
                scales: {
                    xAxes: [{
                        type: 'linear',
                        position: 'bottom',
                        scaleLabel: {
                            display: true,
                            labelString: 'Year Assembly',
                            fontSize: 14
                                    }
                    }],
                    yAxes: [{
                        scaleLabel: {
                            display: true,
                            labelString: 'Aquifer Values',
                            fontSize: 15
                                    }
                    }]
                }
            }
        });
</script>

<script type="text/javascript">
    var xCoord = new Array(1997, 2003, 2005, 2009, 2014, 2018, 2019);
    var yCoord = new Array(41, 31, 11, 31, 88, 101, 91);
    var c = [];
    for (var i = 0; i < xCoord.length; i++) {
        var obj = { x: xCoord[i], y: yCoord[i] };
        c.push(obj);
    }
    var ctx = document.getElementById('myTau').getContext('2d');
    var myTau = new Chart(ctx, {
        type: 'line',
        data: {
            datasets: [{
                label: 'None',
                data: c,
                borderWidth: 1,
                borderColor: "#ef1414",
                fill: false,
                cubicInterpolationMode: 'monotone'
            }
            ]
        },
        options: {
            title: {
                display: true,
                text: 'My Chart 2'
            },
            tooltips: {
                mode: 'nearest',
                intersect: true
            },
            scales: {
                xAxes: [{
                    type: 'linear',
                    position: 'bottom',
                    scaleLabel: {
                        display: true,
                        labelString: 'Year Assembly',
                        fontSize: 14
                    }
                }],
                yAxes: [{
                    scaleLabel: {
                        display: true,
                        labelString: 'Aquifer Values Corresponding',
                        fontSize: 15
                    }
                }]
            }
        }
    });
</script>

Here is problem. The text is written all charts. My aim is only red one chart (My Chart 2).

Place Text in Chart-Canvas Area in ChartJS

2 Answers2

An working example: