Asynchronous charts

Summary: Information about creating your charts using asynchronous HTTP calls. The RGraph.async() method is a simple wrapper around setTimeout(). More efficient methods (eg WebWorkers) may now exist however setTimeout() is simple and effective.

Waiting for onload event...

This image is here to pad the page and slow down loading so that the window.onload event is slowed. This makes the difference far more visible.

Asynchronous processing can speed up the display of your charts, because the browser gets to your code, sets it going and then continues on rendering the page. Particularly if you have a weighty page, it can make quite a difference. The RGraph.async() function itself is very simple, but because it can make a significant difference to the speed of your page, it is documented here. There's an example of it to the right. One thing to remember is to ensure your canvas tag is defined first before you set the function that creates the chart going.

Although asynchronous processing can speed up your pages, it can also give the appearance of slower pages due to partial rendering, (ie your pages render a bit at a time). You therefore will need to experiment to get the best result for you.

<script src="RGraph.common.js"></script>
<script src="RGraph.line.js"></script>

<canvas id="myCanvas" width="300" height="100">[No canvas support]</canvas>

<script>
    /**
    * Create the line chart
    */
    function CreateLineGraph ()
    {
        var line = new RGraph.Line({
            id: 'cvs',
            data: [1,2,4,2,1,3,5,6,6,5,3,5],
            options: {
                title: 'Sales for Acme Inc.',
                xaxisLabels: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
                marginInner: 10,
                linewidth: 5,
                shadowOffsetx: 0,
                shadowOffsety: 0,
                shadowBlur: 15,
                textSize: 14
            }
        }).draw();
    }

    RGraph.async(CreateLineGraph);
</script>

Things to remember

All your libraries must be loaded first. In the pages <head> for example. If not, you won't be able to create your charts.
Your <canvas> tag must be defined before setting the asynchronous code going. If not, then the canvas may be referenced before it exists, and thus your charts will not be created.
The user's connection speed may be a factor. Slower connections may mean, for example, that the load event doesn't fire very quickly. If you're using the load event to create your charts then asynchronous creation instead may give you more apparent speed ups. Alternatively, careful placement of the <canvas> tag and the code that creates the chart may be sufficient instead.

Asynchronous charts

Things to remember

See also