Added Evented#unhookEvent for logic overide

src/event/Evented.js

@@ -259,6 +259,8 @@ module.exports = Trait( 'Evented' )
      * (by not forwarding the listener to __supet) and instead invoke
      * __super with a new listener, possibly wrapping the original.
      *
+     * See also #unhookEvent.
+     *
      * @O {1} constant time
      *
      * @param {string}   ev       defined event id
@@ -328,17 +330,18 @@ module.exports = Trait( 'Evented' )
 
 
     /**
-     * Remove a previously hooked listener in constant time, preventing it
-     * from being invoked on future emits of event EV
+     * Remove a previously hooked listener, preventing it from being invoked
+     * on future emits of event EV
      *
      * EV must be a valid event identifier. If LISTENER is not registered
      * for event id EV, no error will occur (since it fulfills the criteria
      * that it will not be subsequently invoked by event EV).
      *
-     * Listeners are compared by reference---the exact listener that was
-     * registered with EV must be passed for removal.
+     * The default algorithm compares listeners by reference---the exact
+     * listener that was registered with EV must be passed for removal;
+     * note, however, that the algorithm may be overridden by subtypes.
      *
-     * @O {1} constant time
+     * @O {#unhookEvent} depends on unhooking algorithm
      *
      * @param {string}   ev       defined event id
      * @param {Function} listener listener to remove
@@ -353,6 +356,38 @@ module.exports = Trait( 'Evented' )
             throw Error( `Cannot unhook undefined event \`${ev}'` );
         }
 
+        this.unhookEvent( ev, listener );
+        return this;
+    },
+
+
+    /**
+     * Remove a previously hooked listener in constant time, preventing it
+     * from being invoked on future emits of event EV
+     *
+     * Listeners are compared by reference---the exact listener that was
+     * registered with EV must be passed for removal.
+     *
+     * Subtypes may override this method to undo behavior introduced by a
+     * #hookEvent override. Note, however, that the Eventable specification
+     * prohibits removing arbitrary listeners, and so the removed
+     * listener(s) must have somehow been related to LISTENER by #hookEvent.
+     *
+     * This method will be called even if LISTENER has never been attached
+     * to event EV---this method performs that check, ensuring that any
+     * manipulations performed by #hookEvent can be properly handled here.
+     *
+     * See also #hookEvent.
+     *
+     * @O {1} constant time
+     *
+     * @param {string}   ev       defined event id
+     * @param {Function} listener listener to remove
+     *
+     * @return {Evented} self
+     */
+    'virtual protected unhookEvent'( ev, listener )
+    {
         let evls    = this._events[ ev ],
             levdata = listener[ this._evid ] || {},
             index   = levdata[ ev ];

test/event/EventedTest.js

@@ -617,6 +617,109 @@ describe( 'event.Evented', () =>
     } );
 
 
+    /**
+     * Intended to clean up after #hookEvent
+     */
+    describe( '#unhookEvent', function()
+    {
+        var ev  = 'foo',
+            f   = ()=>{};
+
+        it( 'can be overridden by subtypes', ( done ) =>
+        {
+            common.checkOverride( EvStub, 'unhookEvent',
+                ( given_ev, given_listener ) =>
+                {
+                    expect( given_ev ).to.equal( ev );
+                    expect( given_listener ).to.equal( f );
+                    done();
+                }
+            )().evDefineEvents( [ ev ] )
+                .on( ev, f )
+                .removeListener( ev, f );
+        } );
+
+
+        /**
+         * Since #hookEvent can do whatever it pleases with listeners
+         * (including preventing them from being hooked to begin with, or
+         * replacing them with another hook), we need to ensure that the
+         * hook is called regardless of whether the listener is known to be
+         * attached to a particular event; otherwise, certain types of
+         * cleanup would not be possible.
+         */
+        it( 'will be called even if listener is not attached', ( done ) =>
+        {
+            common.checkOverride( EvStub, 'unhookEvent', ( _, __ ) =>
+            {
+                done();
+            } )().evDefineEvents( [ ev ] )
+                .removeListener( ev, f );
+        } );
+
+
+        /**
+         * This should never be done---since it violates the Eventable
+         * specification---but it is useful for determining the scope of the
+         * hook's ability, and is important for proving that, when we modify
+         * the behavior, we know that the default behavior is suppressed
+         * (unless we invoke it ourselves).
+         */
+        it( 'can prevent default implementation', () =>
+        {
+            let norm   = () => called = true,
+                called = false;
+
+            EvStub.extend(
+            {
+                'override unhookEvent': ( _, __ ) => {},
+            } )().evDefineEvents( [ ev ] )
+                .on( ev, norm )
+                .removeListener( ev, norm )
+                .evEmit( ev );
+
+            // should have been called since we suppressed unhooking
+            expect( called ).to.be.true;
+        } );
+
+
+        /**
+         * Listeners must ultimately be added/removed by invoking the super
+         * method (to add listeners to the internal data structures needed
+         * for dispatch on emit). If we are doing any sort of meaningful
+         * manipulation, then we must be able to wholly override the
+         * arguments provided to us.
+         *
+         * As an example, if #hookEvent wrapped the given listener $L$ as
+         * $L'$, which was then hooked for dispatch on some event, then we'd
+         * need to similarily remove $L'$---not $L$---when invoking
+         * #removeListener with $L$.
+         */
+        it( 'can override provided event id and listener', () =>
+        {
+            let rmf    = () => called = true,
+                called = false,
+                ev2    = 'snazzlepuss';
+
+            EvStub.extend(
+            {
+                'override unhookEvent'( _, __ )
+                {
+                    // use these regardless of what we're given
+                    this.__super( ev, rmf );
+                },
+            } )().evDefineEvents( [ ev, ev2 ] )
+                .on( ev, rmf )
+                .removeListener( ev2, f )
+                .evEmit( ev );
+
+            // even though we requested to remove F from some arbitrary
+            // event, our hard-coded removal of RMF should take place
+            expect( called ).to.be.false;
+        } );
+    } );
+
+
     describe( 'listener metadata', () =>
     {
         /**