ChartJs mouse hover bug (showing previous charts)

Question

I think my issue is a known one, everytime I make a new chart and hover my mouse over some points in the canvas, the old charts flash in and out all the time. Here's one of the threads I followed to try and fix it, but nothing seems to work. I tried re-appending the canvas, using destroy, clear, if statements which should clear it, but nothing.

Here's my code:

var ctx = document.getElementById('myChart').getContext('2d');
var myChart = new Chart(ctx, {
    type: 'line',
    data: {
        labels: chartjsDate,
        datasets: [{
            label: 'temp',
            data: chartjsTemp,
            backgroundColor: "rgba(240,240,240,0.5)"
        }]
    }
});

I tried adding myChart.destroy(); before and after that code, even if(myChart!=null){myChart.destroy();}, but still nothing. Any help on how to fix it would be appreciated. All other threads I found are quite old and their solutions don't work.

Edit: Some stuff I tried, to no avail:

var myChart;
if (myChart != undefined || myChart !=null) {
    myChart.destroy();
}

Answer 1

I also had this problem. To solve it, you first have to declare myChart variable globally and then try this way.

//var my chart declare globally.  
let chartData = {
        type: 'line',
        data: {
            labels: chartjsDate,
            datasets: [{
                label: 'temp',
                data: chartjsTemp,
                backgroundColor: "rgba(240,240,240,0.5)"
            }]
        }
        if (typeof(this.myChart) != "undefined") {
            this.myChart.destroy();
        }

        const ctx = this.renderRoot.querySelector('#chart-canvas').getContext('2d');
        this.myChart = new Chart(ctx, chartData);
        this.myChart.update();

Answer 2

Above solutions are working for me but when I have two charts on the same page, Only one is showing. Other charts are becoming empty. Here is the solution for that.

  var ctx = document.getElementById("bar-chart").getContext("2d");  

  //Destroy the previous chart;
  //Rename the "bar" according to your component
  if(window.bar != undefined)
  window.bar.destroy();
  window.bar = new Chart(ctx , {});

if you don't change the "bar", only one chart will show in your page.

Answer 3

It is not bug. Basically you were creating a new graph each time. What you need here is to update graph instead of drawing a new one on that canvas. This can be done using the following code.

 if(typeof Graph ==="undefined"){
       window.Graph = new Chart(Graph_ctx, Graph_config);
 }else{
       //updating with new chart data
       window.Graph.config=Graph_config;
       //redraw the chart
       window.Graph.update();
 }

Answer 4

  var ctxLine = document.getElementById("line-chart").getContext("2d");


 //var myLineChart;
 //myLineChart;
 if(window.bar != undefined)
    window.bar.destroy();
 window.bar = new Chart(ctxLine, {});
 

For more clear check this: solved-hovering-chartjs-bar-chart-showing-old-data

Answer 5

I usually do this before creating my chart

document.querySelector(".chart-container").innerHTML= '<canvas id="bar_chart"></canvas>';
var chart3 = $('#bar_chart');

graph = new Chart(chart3, {
type: 'bar',
data: chart_data,
options: options
});

My html:

<div class="chart-container">
  <canvas id="bar_chart"></canvas>0
</div>

Answer 6

Just Use That and solve your Problem ;

if(window.myChart!=undefined) {
    var oldcanvasid= window.myChart.chart.ctx.canvas.id;
    if(chardcanvasid==oldcanvasid) {
             window.myChart.destroy();
    }
}
var ctx = document.getElementById(chardcanvasid).getContext('2d');
window.myChart = new Chart(ctx, {
   type: charttype,
   data: datass,
   options: optionss,
});