alculating finnish banking reference numbers (Viitenumerot) in javascript, courtesy of jocke.

gistfile1.js

function refnr(source) {
	var chk = 0; 
	var weights = [7,3,1];

	for( var i=0; i<source.length; i++ ) {
		chk += (source[source.length-i-1]-'0')*weights[i%3];
	}

	return source+((10-(chk%10))%10);
}