Fix extend modifying original object / Fix race condition on instance.options

Closes #3457091

js/src/splide.base.js

@@ -93,8 +93,12 @@
     var me = this;
     var root = instance.root;
     var userOptions = $.parse(root.dataset.splide);
-    var opts = $.extend(instance.options, userOptions);
-    var count = opts.count;
+
+    // Need to get a live copy of instance.options as it's modified elsewhere as this runs, and we also want a clone instead of modifying the original.
+    var getMergedOptions = function () {
+      return $.extend({}, instance.options, userOptions);
+    };
+
     var append = function (prev, sel) {
       var el = $.find(root, sel);
       if ($.isElm(el)) {
@@ -115,6 +119,8 @@
     });
 
     instance.on('mounted.' + NICK + ' resized.' + NICK, function () {
+      var opts = getMergedOptions();
+      var count = opts.count;
       $[count <= opts.perPage ? 'addClass' : 'removeClass'](root, IS_LESS);
       $[count > 1 && opts.arrows ? 'addClass' : 'removeClass'](root, IS_ARROWED);
     });
@@ -157,6 +163,8 @@
 
     // Adds arrows down and or pagination inside arrows.
     instance.on('arrows:mounted.' + NICK, function (prev, next) {
+      var opts = getMergedOptions();
+
       if (prev === null) {
         return;
       }
@@ -208,7 +216,8 @@
     if (listeners) {
       $.each(listeners, function (listener) {
         if (listener && typeof listener === 'function') {
-          var fn = listener(instance, instance.Components, o);
+          var opts = getMergedOptions();
+          var fn = listener(instance, instance.Components, opts);
           if ('mount' in fn) {
             fn.mount();
           }