Avoid mutating parameterArray

Author: greg-el

trackers/javascript-tracker/src/in_queue.ts

@@ -266,11 +266,14 @@ export function InQueueManager(functionName: string, asyncQueue: Array<unknown>)
             fnTrackers[tracker.id.replace(`${functionName}_`, '')] = tracker;
           }
 
-          // Append the `fnTrackers` object to the parameterArray, to allow it to be
-          // accessed as the final argument in the callback, useful in environments that don't support `this` (GTM)
-          Array.prototype.push.call(parameterArray, fnTrackers);
+          // Create a new array from `parameterArray` to avoid mutating the original
+          const parameterArrayCopy = Array.prototype.slice.call(parameterArray);
 
-          input.apply(fnTrackers, parameterArray);
+          // Add the `fnTrackers` object as the last element of the new array to allow it to be accessed in the callback
+          // as the final argument, useful in environments that don't support `this` (GTM)
+          const args = Array.prototype.concat.apply(parameterArrayCopy, [fnTrackers]);
+
+          input.apply(fnTrackers, args);
         } catch (ex) {
           LOG.error('Tracker callback failed', ex);
         } finally {