Also test perf of Object.assign

src/util.js

@@ -2,8 +2,19 @@ import { EMPTY_ARR } from './constants';
 
 export const isArray = Array.isArray;
 export const slice = EMPTY_ARR.slice;
-export const assign = Object.assign;
 
+/**
+ * Assign properties from `props` to `obj`
+ * @template O, P The obj and props types
+ * @param {O} obj The object to copy properties to
+ * @param {P} props The object to copy properties from
+ * @returns {O & P}
+ */
+export function assign(obj, props) {
+	// @ts-expect-error We change the type of `obj` to be `O & P`
+	for (let i in props) obj[i] = props[i];
+	return /** @type {O & P} */ (obj);
+}
 /**
  * Remove a child node from its parent if attached. This is a workaround for
  * IE11 which doesn't support `Element.prototype.remove()`. Using this function