how to scan barcode using phonegap
Kris Erickson is correct, the Zxing & Phonegap projects has already taken care of the heavy lifting for you. (My current SO reputation disallows me from commenting, but I would have.)
I've just made an Phonegap/Android app that scans a QR barcode using the plugin here. Follow the instructions and you should be successful. It's possible that the plugin has been written since Kris's answer.
The Javascript is simple, taken straight from https://github.com/phonegap/phonegap-plugins/
var scanBarcode = function() { window.plugins.barcodeScanner.scan( BarcodeScanner.Type.QR_CODE,function(result) { alert("We got a barcode: " + result); }, function(error) { alert("Scanning failed: " + error); }, {yesString: "Install"} ); }
This link leads you to a page where you can learn how to implement the PhoneGap Barcode Scanner plugin in your application