app-app-store-argument.js

function getParameterByName(name) {
    name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
        results = regex.exec(location.search);
    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}
var meta = document.getElementsByTagName('meta');
var apple_launch_elem;
for (var i=0;i < meta.length; i++) {
	var elem = meta[i];
	if (elem.getAttribute('name') === 'apple-itunes-app') {
		apple_launch_elem = elem;
	}
}
var launchurl = getParameterByName('launchurl');
if (apple_launch_elem) {
	var tmp = apple_launch_elem.getAttribute('content');
	apple_launch_elem.setAttribute('content', tmp + ', app-argument=' + decodeURIComponent(launchurl));
}

app-store-argument-in-document-write.html

<script>
function getParameterByName(name) {
    name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
        results = regex.exec(location.search);
    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}
var appleAppStoreID = "298307011";
var playLink = getParameterByName('launchurl');
document.writeln('<meta name="apple-itunes-app" content="app-id='+appleAppStoreID+', app-argument='+playLink+'" \/>');
</script>