function which takes two expressions and binds them together (useful for date processing)

bindToSeparateDateFieldFactory.js

function bindToSeparateDateFieldFactory ($rootScope, $parse) {
	return function (context, srcExpression, targetExpression) {
		var getTarget = $parse(targetExpression),
			setTarget = getTarget.assign,
			getSrc = $parse(srcExpression),
			setSrc = getSrc.assign;

		$rootScope.$watch(
			function () { return getTarget(context); },
			function (newValue) { newValue && setSrc(context, newValue + 'T00:00:00.000Z'); }
		);
		$rootScope.$watch(
			function () { return getSrc(context); },
			function (newValue) { newValue && setTarget(context, newValue.substr(0, 10)); }
		);
	};
}

this.invoiceIssuedOn = null;

bindToSeparateDateField(this, 'invoice.issuedOn', 'invoiceIssuedOn');