parseBindingAttr for angular

parseBindingAttr

/** By J.louis */
function parseExprAttr($parse, $scope, $attrs, name) {
	var fn = $parse($attrs[name]),
		res
	;
	res = function (locals) {
		return fn($scope, locals);
	};
	res.assign = fn.assign && function (value) {
		fn.assign($scope, value);
	};
	return res;
}

function parseBindingAttr($parse, $scope, $attrs, name, optional) {
	var res;
	if (!(name in $attrs)) {
		if (!optional) {
			throw new Error(name + ' attribute must be specified');
		}

		let value;
		res = function () {
			return value;
		};
		res.assign = function (v) {
			value = v;
		};
		return res;
	}

	res = parseExprAttr($parse, $scope, $attrs, name);
	if (!res.assign) {
		throw new Error(name + ' model must be assignable');
	}

	return res;
}