Creating charts asynchronously
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.',
titleSize: 16,
titleBold: true,
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,
textAccessible: false,
xaxis: false,
yaxis: false,
backgroundGridVlines: false,
backgroundGridBorder: false
}
}).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 theload
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.