feat: add eventEmitter (#1693)

perrin4869 · web-flow · commit c22027c4c25a · 2025-08-25T11:46:16.000+01:00
Adds an event emitter for hooking into method/property creation
diff --git a/eslint.config.js b/eslint.config.js
@@ -1,5 +1,6 @@
 import jsdoc from "eslint-plugin-jsdoc";
 import eslintjs from "@eslint/js";
+import globals from "globals";
 
 const {configs: eslintConfigs} = eslintjs;
 
@@ -8,9 +9,9 @@ export default [
   eslintConfigs["recommended"],
   {
     languageOptions: {
-      // if we ever use more globals than this, pull in the `globals` package
       globals: {
-        console: false
+        console: false,
+        ...globals.browser, // EventTarget, Event
       }
     },
     rules: {
diff --git a/lib/chai/utils/addMethod.js b/lib/chai/utils/addMethod.js
@@ -5,6 +5,7 @@
  */
 
 import {addLengthGuard} from './addLengthGuard.js';
+import {PluginEvent, events} from './events.js';
 import {flag} from './flag.js';
 import {proxify} from './proxify.js';
 import {transferFlags} from './transferFlags.js';
@@ -63,4 +64,6 @@ export function addMethod(ctx, name, method) {
 
   addLengthGuard(methodWrapper, name, false);
   ctx[name] = proxify(methodWrapper, name);
+
+  events.dispatchEvent(new PluginEvent('addMethod', name, method));
 }
diff --git a/lib/chai/utils/addProperty.js b/lib/chai/utils/addProperty.js
@@ -5,6 +5,7 @@
  */
 
 import {Assertion} from '../assertion.js';
+import {PluginEvent, events} from './events.js';
 import {flag} from './flag.js';
 import {isProxyEnabled} from './isProxyEnabled.js';
 import {transferFlags} from './transferFlags.js';
@@ -67,4 +68,6 @@ export function addProperty(ctx, name, getter) {
     },
     configurable: true
   });
+
+  events.dispatchEvent(new PluginEvent('addProperty', name, getter));
 }
diff --git a/lib/chai/utils/events.js b/lib/chai/utils/events.js
@@ -0,0 +1,16 @@
+/*!
+ * Chai - events utility
+ * Copyright(c) 2011-2016 Jake Luer <jake@alogicalparadox.com>
+ * MIT Licensed
+ */
+
+// Global EventTarget instance
+export const events = new EventTarget();
+
+export class PluginEvent extends Event {
+  constructor(type, name, fn) {
+    super(type);
+    this.name = String(name);
+    this.fn = fn;
+  }
+}
diff --git a/lib/chai/utils/index.js b/lib/chai/utils/index.js
@@ -96,6 +96,9 @@ export {isNaN} from './isNaN.js';
 // getOperator method
 export {getOperator} from './getOperator.js';
 
+// events EventTarget
+export {events} from './events.js';
+
 /**
  * Determines if an object is a `RegExp`
  * This is used since `instanceof` will not work in virtual contexts
diff --git a/package-lock.json b/package-lock.json
diff --git a/package.json b/package.json
@@ -61,6 +61,7 @@
     "esbuild": "^0.25.9",
     "eslint": "^8.56.0",
     "eslint-plugin-jsdoc": "^48.0.4",
+    "globals": "^16.3.0",
     "loupe": "^3.1.0",
     "mocha": "^10.2.0",
     "pathval": "^2.0.0",
diff --git a/test/utilities.js b/test/utilities.js
@@ -1503,4 +1503,54 @@ describe('utilities', function () {
       });
     });
   });
+
+  describe('eventEmitter', function() {
+    var eventHandler = null;
+
+    beforeEach(function() {
+      if (eventHandler) {
+        chai.util.events.removeEventListener("addMethod", eventHandler);
+        chai.util.events.removeEventListener("addProperty", eventHandler);
+      }
+      eventHandler = null;
+      delete chai.Assertion.prototype.eqqqual;
+      delete chai.Assertion.prototype.tea;
+    });
+
+    it('emits addMethod', function () {
+      var calledTimes = 0;
+
+      chai.use(function(_chai, _utils) {
+        const eqqqual = function (str) {
+          var object = _utils.flag(this, 'object');
+          new _chai.Assertion(object).to.be.eql(str);
+        }
+        chai.util.events.addEventListener("addMethod", eventHandler = function({ name, fn }) {
+          if (name === 'eqqqual' && fn === eqqqual)
+            calledTimes++;
+        });
+        _chai.Assertion.addMethod('eqqqual', eqqqual);
+      });
+
+      expect(calledTimes).to.equal(1);
+    });
+
+    it('emits addProperty', function () {
+      var calledTimes = 0;
+
+      chai.use(function(_chai, _utils) {
+        const getter = function () {
+          return 'chai';
+        }
+        chai.util.events.addEventListener("addProperty", eventHandler = function({ name, fn }) {
+          if (name === 'tea' && fn === getter)
+            calledTimes++;
+        });
+        _chai.Assertion.addProperty('tea', getter);
+
+      });
+
+      expect(calledTimes).to.equal(1);
+    });
+  });
 });
