1 files changed, 25 insertions, 0 deletions
diff --git a/js/src/tests/non262/Array/concat-proxy.js b/js/src/tests/non262/Array/concat-proxy.js
new file mode 100644
index 0000000000..ab733e2f10
--- /dev/null
+++ b/js/src/tests/non262/Array/concat-proxy.js
@@ -0,0 +1,25 @@
+var BUGNUMBER = 1287520;
+var summary = 'Array.prototype.concat should check HasProperty everytime for non-dense array';
+
+print(BUGNUMBER + ": " + summary);
+
+var a = [1, 2, 3];
+a.constructor = {
+  [Symbol.species]: function(...args) {
+    var p = new Proxy(new Array(...args), {
+      defineProperty(target, propertyKey, receiver) {
+        if (propertyKey === "0") delete a[1];
+        return Reflect.defineProperty(target, propertyKey, receiver);
+      }
+    });
+    return p;
+  }
+};
+
+var p = a.concat();
+assertEq(0 in p, true);
+assertEq(1 in p, false);
+assertEq(2 in p, true);
+
+if (typeof reportCompare === "function")
+  reportCompare(true, true);