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packages/@ember/-internals/utils/lib/mandatory-setter.ts

@@ -14,6 +14,19 @@ export let setWithMandatorySetter:
 
 type PropertyDescriptorWithMeta = PropertyDescriptor & { hadOwnProperty?: boolean };
 
+function isElementKey(key: string | number | symbol) {
+  return typeof key === 'number' ? isPositiveInt(key) : isStringInt(key as string);
+}
+
+function isStringInt(str: string) {
+  let num = parseInt(str, 10);
+  return isPositiveInt(num) && str === String(num);
+}
+
+function isPositiveInt(num: number) {
+  return num >= 0 && num % 1 === 0;
+}
+
 if (DEBUG) {
   let SEEN_TAGS = new WeakSet();
 
@@ -34,9 +47,8 @@ if (DEBUG) {
 
     SEEN_TAGS!.add(tag);
 
-    if (Array.isArray(obj) && !isNaN(Number(keyName))) {
-      // don't setup mandatory setter, arrays can remove property descriptors
-      // themselves and we can't control them correctly.
+    if (Array.isArray(obj) && !isElementKey(keyName)) {
+      // this would replace the conditional
       return;
     }