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qwen/nodejs/node_modules/eslint/lib/linter/safe-emitter.js

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+/**
+ * @fileoverview A variant of EventEmitter which does not give listeners information about each other
+ * @author Teddy Katz
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Typedefs
+//------------------------------------------------------------------------------
+
+/**
+ * An event emitter
+ * @typedef {Object} SafeEmitter
+ * @property {(eventName: string, listenerFunc: Function) => void} on Adds a listener for a given event name
+ * @property {(eventName: string, arg1?: any, arg2?: any, arg3?: any) => void} emit Emits an event with a given name.
+ * This calls all the listeners that were listening for that name, with `arg1`, `arg2`, and `arg3` as arguments.
+ * @property {function(): string[]} eventNames Gets the list of event names that have registered listeners.
+ */
+
+/**
+ * Creates an object which can listen for and emit events.
+ * This is similar to the EventEmitter API in Node's standard library, but it has a few differences.
+ * The goal is to allow multiple modules to attach arbitrary listeners to the same emitter, without
+ * letting the modules know about each other at all.
+ * 1. It has no special keys like `error` and `newListener`, which would allow modules to detect when
+ * another module throws an error or registers a listener.
+ * 2. It calls listener functions without any `this` value. (`EventEmitter` calls listeners with a
+ * `this` value of the emitter instance, which would give listeners access to other listeners.)
+ * @returns {SafeEmitter} An emitter
+ */
+module.exports = () => {
+    const listeners = Object.create(null);
+
+    return Object.freeze({
+        on(eventName, listener) {
+            if (eventName in listeners) {
+                listeners[eventName].push(listener);
+            } else {
+                listeners[eventName] = [listener];
+            }
+        },
+        emit(eventName, ...args) {
+            if (eventName in listeners) {
+                listeners[eventName].forEach(listener => listener(...args));
+            }
+        },
+        eventNames() {
+            return Object.keys(listeners);
+        }
+    });
+};