Make evented#addEventListener idempotent

mapbox · May 17, 2018 · a5da36c · a5da36c
1 parent 9d9ec49
commit a5da36c
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diff --git a/src/util/evented.js b/src/util/evented.js
@@ -6,6 +6,7 @@ type Listener = (Object) => any;
 type Listeners = { [string]: Array<Listener> };
 
 function _addEventListener(type: string, listener: Listener, listenerList: Listeners) {
+    _removeEventListener(type, listener, listenerList);
     listenerList[type] = listenerList[type] || [];
     listenerList[type].push(listener);
 }

diff --git a/test/unit/util/evented.test.js b/test/unit/util/evented.test.js
@@ -119,6 +119,17 @@ test('Evented', (t) => {
         t.end();
     });
 
+    t.test('on is idempotent', (t) => {
+      const evented = new Evented();
+      const listener = t.spy();
+      evented.on('a', listener);
+      evented.on('a', listener);
+      evented.on('a', listener);
+      evented.fire(new Event('a'));
+      t.ok(listener.calledOnce);
+      t.end();
+    });
+
     t.test('evented parents', (t) => {
 
         t.test('adds parents with "setEventedParent"', (t) => {