object type checking with recursion

typecheck.js

// checks if an object's data is symmetric with a struct with defining types
function typecheck(object, types, optional=null) {
	// TODO: optional error print, showing
	// where in the object did this function fail
	// if that's even possible
	//
	// example:
	//	typecheck({
	//		"thing": 1,
	//		"thing2": "2",
	//		"thing3": {
	//			"thing4": [ "4", -4, 4 ],
	//			"thing5": {
	//				"param": {
	//					"within_another": 4
	//				}
	//			}
	//		}
	//	}, {
	//		"thing": "number",
	//		"thing2": "string",
	//		"thing3": {
	//			"thing4": [ "*" ],
	//			"thing5": {
	//				"param": {
	//					"within_another": "number"
	//				}
	//			}
	//		}
	//	});
	//
	'use strict';
	if (Array.isArray(types))
	{
		// `types` at this point must contain a singular element that has
		// the type string to match the type of the elements inside the object
		// i.e. [ 0, 1, 2, 3 ] == [ 'number' ]
		//
		// use [ '*' ] to contain elements of any type
		if (Array.isArray(object)) {
			if (types.length === 1) {
				// support alternating types with modulo?
				// (like ['number', 'string', 'number'])
				if (types[0] === '*') return true;
				for (var i = 0; i < object.length; i++)
					if (!typecheck(object[i], types[0]))
						return false;
				return true;
			}
			else
				throw "Type object "+JSON.stringify(types)+
						"is an invalid array to test against "+JSON.stringify(object);
		}
	} else if (types.toString() === '[object Object]') {
		var all_keys = [...new Set([...Object.keys(object), ...Object.keys(types)])];
		for (var i = 0; i < all_keys.length; i++) {
			var o = all_keys[i];
			if (!types.hasOwnProperty(o))
				return false;
			if (!object.hasOwnProperty(o) && !(optional === null || !optional[o]))
				continue; // skip if optional item not in object
			if (!typecheck(object[o], types[o],
				optional !== null && optional.hasOwnProperty(o) ? optional[o] : null))
				return false;
		}
		return true;
	}
	return typeof object === types.toString() || types === "*";
	// if type = 'object', any type of struct
	// is accepted, or allow anything if = '*'
}