resolves katspaugh#660; cancel ajax on destroy/empty

src/wavesurfer.js

@@ -64,12 +64,17 @@ var WaveSurfer = {
         // Used to save the current volume when muting so we can
         // restore once unmuted
         this.savedVolume = 0;
+
         // The current muted state
         this.isMuted = false;
+
         // Will hold a list of event descriptors that need to be
         // cancelled on subsequent loads of audio
         this.tmpEvents = [];
 
+        // Holds any running audio downloads
+        this.currentAjax = null;
+
         this.createDrawer();
         this.createBackend();
     },
@@ -390,19 +395,28 @@ var WaveSurfer = {
 
     getArrayBuffer: function (url, callback) {
         var my = this;
+
         var ajax = WaveSurfer.util.ajax({
             url: url,
             responseType: 'arraybuffer'
         });
+
+        this.currentAjax = ajax;
+
         this.tmpEvents.push(
             ajax.on('progress', function (e) {
                 my.onProgress(e);
             }),
-            ajax.on('success', callback),
+            ajax.on('success', function (data, e) {
+                callback(data);
+                my.currentAjax = null;
+            }),
             ajax.on('error', function (e) {
                 my.fireEvent('error', 'XHR error: ' + e.target.statusText);
+                my.currentAjax = null;
             })
         );
+
         return ajax;
     },
 
@@ -436,6 +450,13 @@ var WaveSurfer = {
         return json;
     },
 
+    cancelAjax: function () {
+        if (this.currentAjax) {
+            this.currentAjax.xhr.abort();
+            this.currentAjax = null;
+        }
+    },
+
     clearTmpEvents: function () {
         this.tmpEvents.forEach(function (e) { e.un(); });
     },
@@ -448,6 +469,7 @@ var WaveSurfer = {
             this.stop();
             this.backend.disconnectSource();
         }
+        this.cancelAjax();
         this.clearTmpEvents();
         this.drawer.progress(0);
         this.drawer.setWidth(0);
@@ -459,6 +481,7 @@ var WaveSurfer = {
      */
     destroy: function () {
         this.fireEvent('destroy');
+        this.cancelAjax();
         this.clearTmpEvents();
         this.unAll();
         this.backend.destroy();