Here is the tracking issue for this feature request.
As an workaround, you can send API request like this:
{
template: {
....
phantom: {
viewportSize: {
width: 1000,
height: 1000
}
}
}
}
When working with jsreport studio, you can create a custom script like this:
function beforeRender(req, res, done) {
if (...)
req.template.phantom.viewportSize = {
width: 1000,
height: 1000
}
done()
}