Utils.Array.Flatten is a new function that will return a flattened version of an array, regardless of how deeply-nested it is.

src/utils/array/Flatten.js

@@ -0,0 +1,37 @@
+/**
+ * @author       Richard Davey <rich@photonstorm.com>
+ * @copyright    2022 Photon Storm Ltd.
+ * @license      {@link https://opensource.org/licenses/MIT|MIT License}
+ */
+
+/**
+ * Takes an array and flattens it, returning a shallow-copy flattened array.
+ *
+ * @function Phaser.Utils.Array.Flatten
+ * @since 3.60.0
+ *
+ * @param {array} array - The array to flatten.
+ * @param {array} [output] - An array to hold the results in.
+ *
+ * @return {array} The flattened output array.
+ */
+var Flatten = function (array, output)
+{
+    if (output === undefined) { output = []; }
+
+    for (var i = 0; i < array.length; i++)
+    {
+        if (Array.isArray(array[i]))
+        {
+            Flatten(array[i], output);
+        }
+        else
+        {
+            output.push(array[i]);
+        }
+    }
+
+    return output;
+};
+
+module.exports = Flatten;

src/utils/array/index.js

@@ -19,6 +19,7 @@ module.exports = {
     Each: require('./Each'),
     EachInRange: require('./EachInRange'),
     FindClosestInSorted: require('./FindClosestInSorted'),
+    Flatten: require('./Flatten'),
     GetAll: require('./GetAll'),
     GetFirst: require('./GetFirst'),
     GetRandom: require('./GetRandom'),