[Chartjs]-Chart.js – Creating multiple charts on one page

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You are redeclaring window.onload function. Thats why you will draw only one (last) chart.

window.onload = function(){ 
    var ctx_$title = document.getElementById('canvas_$title').getContext('2d');                                    
    window.myBar = new Chart(ctx_$title).Bar(barChartData_$title, { responsive : true }); 

}

What you can do to fix that. Im proposing to change JHtmlGraphs class as following:

    abstract class JHtmlGraphs 
{
    private $titles = array();

    public function draw($title = NULL, $labelset = NULL, $data = NULL, $data2 = NULL)
    {
        $script = "<script> var barChartData_$title = { labels : [ {$labelset} ], datasets : [ { fillColor : 'rgba(220,220,220,0.5)', strokeColor : 'rgba(220,220,220,0.8)', highlightFill: 'rgba(220,220,220,0.75)', highlightStroke: 'rgba(220,220,220,1)', data : [ $data ] }, { fillColor : 'rgba(151,187,205,0.5)', strokeColor : 'rgba(151,187,205,0.8)', highlightFill : 'rgba(151,187,205,0.75)', highlightStroke : 'rgba(151,187,205,1)', data : [ $data2 ] } ] };</script>";
        $canvas = "<div style='width: 100%'><canvas id='canvas_$title' height='20' width='20'></canvas></div>";

        $this->titles[] = $title; //storing titles
        return $script . $canvas;
    }

    public function finishDrawing() {
        $launchCharts = '';
        foreach($this->titles as $title) {
            $launchCharts .= "var ctx_$title = document.getElementById('canvas_$title').getContext('2d'); window.myBar_$title = new Chart(ctx_$title).Bar(barChartData_$title, { responsive : true });";
        }
        $this->titles = array();

        $script =  "<script>window.onload = function(){ $launchCharts }</script>";
        return $script;
    }
}

I modified your scripts. Now your onload function will be generated one time, from finishDrawing method:

<?php echo JHtml::_('graphs.draw', "Titel", $labelset, $data, $data2);  ?>
<?php echo JHtml::_('graphs.draw', "Titel2", $labelset, $data, $data2); ?>

And somewhere at the bottom you have to call new function:

<?php echo JHtml::finishDrawing(); //you better know than me how to call this function?>

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