1 files changed, 22 insertions, 0 deletions
diff --git a/js/src/tests/non262/lexical-environment/unscopables-basics.js b/js/src/tests/non262/lexical-environment/unscopables-basics.js
new file mode 100644
index 0000000000..4032b27746
--- /dev/null
+++ b/js/src/tests/non262/lexical-environment/unscopables-basics.js
@@ -0,0 +1,22 @@
+// Basics of @@unscopables support.
+
+// In with(obj), if obj[@@unscopables][id] is truthy, then the identifier id
+// is not present as a binding in the with-block's scope.
+var x = "global";
+with ({x: "with", [Symbol.unscopables]: {x: true}})
+    assertEq(x, "global");
+
+// But if obj[@@unscopables][id] is false or not present, there is a binding.
+with ({y: "with", z: "with", [Symbol.unscopables]: {y: false}}) {
+    assertEq(y, "with");
+    assertEq(z, "with");
+}
+
+// ToBoolean(obj[@@unscopables][id]) determines whether there's a binding.
+let someValues = [0, -0, NaN, "", undefined, null, "x", {}, []];
+for (let v of someValues) {
+    with ({x: "with", [Symbol.unscopables]: {x: v}})
+        assertEq(x, v ? "global" : "with");
+}
+
+reportCompare(0, 0);