From fe83d1b32c1c69134c6221b39951d784a00bdbd4 Mon Sep 17 00:00:00 2001
From: ahocevar <andreas.hocevar@gmail.com>
Date: Thu, 29 Aug 2019 22:35:32 +0200
Subject: [PATCH] Only bind listeners when necessary

---
 src/ol/events.js            | 21 +++++++++++++--------
 test/spec/ol/events.test.js | 24 ++++++++++++------------
 2 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/src/ol/events.js b/src/ol/events.js
index 200b048058..02a9b6a224 100644
--- a/src/ol/events.js
+++ b/src/ol/events.js
@@ -32,14 +32,19 @@ import {clear} from './obj.js';
  * @return {ListenerFunction} Bound listener.
  */
 export function bindListener(listenerObj) {
-  const boundListener = function(evt) {
-    const listener = listenerObj.listener;
-    const bindTo = listenerObj.bindTo || listenerObj.target;
-    if (listenerObj.callOnce) {
-      unlistenByKey(listenerObj);
-    }
-    return listener.call(bindTo, evt);
-  };
+  let boundListener;
+  if (listenerObj.bindTo || listenerObj.callOnce) {
+    boundListener = function(evt) {
+      const listener = listenerObj.listener;
+      const bindTo = listenerObj.bindTo || listenerObj.target;
+      if (listenerObj.callOnce) {
+        unlistenByKey(listenerObj);
+      }
+      return listener.call(bindTo, evt);
+    };
+  } else {
+    boundListener = listenerObj.listener;
+  }
   listenerObj.boundListener = boundListener;
   return boundListener;
 }
diff --git a/test/spec/ol/events.test.js b/test/spec/ol/events.test.js
index 2c56d0de75..5430e72956 100644
--- a/test/spec/ol/events.test.js
+++ b/test/spec/ol/events.test.js
@@ -24,15 +24,14 @@ describe('ol.events', function() {
       boundListener();
       expect(listenerObj.listener.thisValues[0]).to.equal(listenerObj.bindTo);
     });
-    it('binds to the target when bindTo is not provided', function() {
-      const listenerObj = {
-        listener: sinon.spy(),
-        target: {id: 1}
-      };
-      const boundListener = bindListener(listenerObj);
-      expect(listenerObj.boundListener).to.equal(boundListener);
-      boundListener();
-      expect(listenerObj.listener.thisValues[0]).to.equal(listenerObj.target);
+    it('binds to the target when bindTo is not provided', function(done) {
+      const target = new EventTarget();
+      const listenerObj = listen(target, 'foo', function() {
+        expect(this).to.equal(target);
+        done();
+      });
+      expect(listenerObj.boundListener).to.equal(listenerObj.listener);
+      target.dispatchEvent('foo');
     });
     it('binds a self-unregistering listener when callOnce is true', function() {
       const bindTo = {id: 1};
@@ -122,13 +121,14 @@ describe('ol.events', function() {
 
   describe('listenOnce()', function() {
     it('creates a one-off listener', function() {
+      const target = new EventTarget();
       const listener = sinon.spy();
       const key = listenOnce(target, 'foo', listener);
-      expect(add.callCount).to.be(1);
       expect(key.callOnce).to.be(true);
-      key.boundListener();
+      target.dispatchEvent('foo');
+      expect(listener.callCount).to.be(1);
+      target.dispatchEvent('foo');
       expect(listener.callCount).to.be(1);
-      expect(remove.callCount).to.be(1);
     });
     it('does not add the same listener twice', function() {
       const listener = function() {};