Add more specific check for constructors than simply checking if it's…

… a function when registering components in the registry (#179)

* Replaced simple function checks for actual checks that the function is a constructor of a subclass of Command in the registry loader functions

* Added isConstructor checks for groups and types as well

src/registry.js

@@ -4,6 +4,7 @@ const Command = require('./commands/base');
 const CommandGroup = require('./commands/group');
 const CommandoMessage = require('./extensions/message');
 const ArgumentType = require('./types/base');
+const { isConstructor } = require('./util');
 
 /** Handles registration and searching of commands and groups */
 class CommandoRegistry {
@@ -59,7 +60,7 @@ class CommandoRegistry {
 	registerGroup(group, name, guarded) {
 		if(typeof group === 'string') {
 			group = new CommandGroup(this.client, group, name, guarded);
-		} else if(typeof group === 'function') {
+		} else if(isConstructor(group, CommandGroup)) {
 			group = new group(this.client); // eslint-disable-line new-cap
 		} else if(typeof group === 'object' && !(group instanceof CommandGroup)) {
 			group = new CommandGroup(this.client, group.id, group.name, group.guarded);
@@ -118,10 +119,9 @@ class CommandoRegistry {
 	 */
 	registerCommand(command) {
 		/* eslint-disable new-cap */
-		if(typeof command === 'function') command = new command(this.client);
-		else if(typeof command.default === 'function') command = new command.default(this.client);
+		if(isConstructor(command, Command)) command = new command(this.client);
+		else if(isConstructor(command.default, Command)) command = new command.default(this.client);
 		/* eslint-enable new-cap */
-
 		if(!(command instanceof Command)) throw new Error(`Invalid command object to register: ${command}`);
 
 		// Make sure there aren't any conflicts
@@ -167,7 +167,7 @@ class CommandoRegistry {
 	registerCommands(commands, ignoreInvalid = false) {
 		if(!Array.isArray(commands)) throw new TypeError('Commands must be an Array.');
 		for(const command of commands) {
-			const valid = typeof command === 'function' || typeof command.default === 'function' ||
+			const valid = isConstructor(command, Command) || isConstructor(command.default, Command) ||
 				command instanceof Command || command.default instanceof Command;
 			if(ignoreInvalid && !valid) {
 				this.client.emit('warn', `Attempting to register an invalid command object: ${command}; skipping.`);
@@ -208,8 +208,8 @@ class CommandoRegistry {
 	 */
 	registerType(type) {
 		/* eslint-disable new-cap */
-		if(typeof type === 'function') type = new type(this.client);
-		else if(typeof type.default === 'function') type = new type.default(this.client);
+		if(isConstructor(type, ArgumentType)) type = new type(this.client);
+		else if(isConstructor(type.default, ArgumentType)) type = new type.default(this.client);
 		/* eslint-enable new-cap */
 
 		if(!(type instanceof ArgumentType)) throw new Error(`Invalid type object to register: ${type}`);
@@ -241,7 +241,7 @@ class CommandoRegistry {
 	registerTypes(types, ignoreInvalid = false) {
 		if(!Array.isArray(types)) throw new TypeError('Types must be an Array.');
 		for(const type of types) {
-			const valid = typeof type === 'function' || typeof type.default === 'function' ||
+			const valid = isConstructor(type, ArgumentType) || isConstructor(type.default, ArgumentType) ||
 				type instanceof ArgumentType || type.default instanceof ArgumentType;
 			if(ignoreInvalid && !valid) {
 				this.client.emit('warn', `Attempting to register an invalid argument type object: ${type}; skipping.`);
@@ -384,8 +384,8 @@ class CommandoRegistry {
 	 */
 	reregisterCommand(command, oldCommand) {
 		/* eslint-disable new-cap */
-		if(typeof command === 'function') command = new command(this.client);
-		else if(typeof command.default === 'function') command = new command.default(this.client);
+		if(isConstructor(command, Command)) command = new command(this.client);
+		else if(isConstructor(command.default, Command)) command = new command.default(this.client);
 		/* eslint-enable new-cap */
 
 		if(command.name !== oldCommand.name) throw new Error('Command name cannot change.');

src/util.js

@@ -1,3 +1,7 @@
+// This returns Object.prototype in order to return a valid object
+// without creating a new one each time this is called just to discard it the moment after.
+const isConstructorProxyHandler = { construct() { return Object.prototype; } };
+
 function escapeRegex(str) {
 	return str.replace(/[|\\{}()[\]^$+*?.]/g, '\\$&');
 }
@@ -7,6 +11,17 @@ function disambiguation(items, label, property = 'name') {
 	return `Multiple ${label} found, please be more specific: ${itemList}`;
 }
 
+function isConstructor(func, _class) {
+	try {
+		// eslint-disable-next-line no-new
+		new new Proxy(func, isConstructorProxyHandler)();
+		if(!_class) return true;
+		return func.prototype instanceof _class;
+	} catch(err) {
+		return false;
+	}
+}
+
 function paginate(items, page = 1, pageLength = 10) {
 	const maxPage = Math.ceil(items.length / pageLength);
 	if(page < 1) page = 1;
@@ -55,5 +70,6 @@ module.exports = {
 	escapeRegex,
 	disambiguation,
 	paginate,
-	permissions
+	permissions,
+	isConstructor
 };