function Permissions() {
}

Permissions.createRules = function(options) {
	var permissions = {};
	var num = 1;
	var len = options.length;
	for(var i=0;i<len;i++) {
		if(i === 0) {
			permissions[options[i]] = num;
		} else {
			num *= 2;
			permissions[options[i]] = num;
		}
	}
	return permissions;
}

Permissions.createPermissions = function (rules) {
	var result = 0;
	var len = rules.length;
	for(var i=0;i<len;i++) {
		result ^= rules[i];
	}
	return result;
}

Permissions.checkPermission = function(permissions, rule) {
	return Boolean(permissions & rule);
}

var rules = Permissions.createRules(['view', 'modify', 'create', 'delete']);
var permissions = Permissions.createPermissions([rules.modify, rules.delete]);
console.log('#view', Permissions.checkPermission(permissions, rules.view));
console.log('#modify', Permissions.checkPermission(permissions, rules.modify));
console.log('#create', Permissions.checkPermission(permissions, rules.create));
console.log('#delete', Permissions.checkPermission(permissions, rules.delete));