How can I see print preview of my invoice generated from website. If I print with the script
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You can create separate print stylesheets to have some general control over how a site will look in print. You can display the site to your user using this special print stylesheet before printing. That does not give you a 100% preview though, as every browser handles things a bit differently. You won't see how it prints until it actually prints. Using a print stylesheet will get you pretty close though.
Some operating systems and printer drivers offer a preview to the user between hitting the Print button and the actual print, but that's not something you have control over or that's guaranteed to always be available.