Add documentation and change object to map.

src/modules/hooks/base_hooks.js

@@ -1,55 +1,103 @@
 module.exports = class BaseHooks {
   constructor() {
-    this._events = {};
+    /**
+     * @type {Map.<string, Set.<Function>>} A map between an event name to a set of callbacks registered for it.
+     * Function shape varies between different events.
+     * @private
+     */
+    this._events = new Map();
   }
 
+  /**
+   * Registers a callback or array of callbacks to an event.
+   * Callback function shape may vary according to the event type.
+   * Upon a hook trigger, the callbacks for it will be invoked one by one, but without a particular order.
+   * The user who registers the callback has the responsibility to handle any error inside of it. Throwing an error inside a callback will propagate it outside to the top level, aborting the process that triggered it.
+   * @param {string} event The event name to register.
+   * @param {(Function|Function[])} callback A callback or array of callbacks to register for the event.
+   * @protected
+   */
   _on(event, callback) {
     if (Array.isArray(callback)) {
       this._manyOn(event, callback);
       return;
     }
 
-    if (!this._events[event]) {
-      this._events[event] = new Set();
-    }
-    this._events[event].add(callback);
+    this._getCallbacks(event).add(callback);
   }
 
+  /**
+   * Registers a number of callbacks for an event.
+   * @param {string} event The event name to register.
+   * @param {Function|Function[]} callbacks A callback array register for the event.
+   * @private
+   */
   _manyOn(event, callbacks) {
-    if (!this._events[event]) {
-      this._events[event] = new Set();
-    }
-    callbacks.forEach((callback) => this._events[event].add(callback));
+    const registered = this._getCallbacks(event);
+    callbacks.forEach((callback) => registered.add(callback));
   }
 
+  /**
+   * Unregister a callback or array of callbacks from an event.
+   * Callbacks must be a reference to the same callbacks that registered.
+   * @param {string} event The event to unregister.
+   * @param {(Function|Function[])} callback A callback or array of callbacks to unregistered from the event.
+   * @protected
+   */
   _off(event, callback) {
     if (Array.isArray(callback)) {
       this._manyOff(event, callback);
       return;
     }
 
-    if (!this._events[event]) {
+    const callbacks = this._getCallbacks();
+    if (callbacks) {
       return;
     }
-    this._events[event].delete(callback);
+    callbacks.delete(callback);
   }
 
+  /**
+   * Unregister a number of callbacks from an event.
+   * @param {string} event The event to unregister.
+   * @param {Function[]} callbacks A callback array to unregistered from the event.
+   * @private
+   */
   _manyOff(event, callbacks) {
-    if (!this._events[event]) {
+    const registered = this._getCallbacks();
+    if (registered) {
       return;
     }
-    callbacks.forEach((callback) => this._events[event].delete(callback));
+    callbacks.forEach((callback) => registered.delete(callback));
   }
 
+  /**
+   * Trigger an event, calling all callbacks registered to it with the given payload.
+   * @param {*} source The class/object that triggered the event. Will be bound as the 'this' argument of the callbacks.
+   * @param {string} eventName The name of the event to trigger.
+   * @param {*} payload The event to pass to the registered callbacks as an argument.
+   * @public
+   */
   async trigger(source, eventName, payload) {
-    if (!this._events[eventName]) {
+    const callbacks = this._getCallbacks(eventName);
+    if (!callbacks) {
       return;
     }
 
     // This rule intends to restrict it for arrays, but this is a Set which doesn't have a '.map' function to use instead.
     // eslint-disable-next-line no-restricted-syntax
-    for (const callback of this._events[eventName]) {
+    for (const callback of callbacks) {
       await callback.call(source, payload);
     }
   }
+
+  /** @private */
+  _getCallbacks(event) {
+    let callbacks = this._events.get(event);
+    if (!callbacks) {
+      callbacks = new Set();
+      this._events.set(event, callbacks);
+    }
+    return callbacks;
+  }
 };