LibJS: Throw TypeError on write to non-writable property in strict mode

1 files changed, 12 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Tests/non-writable-assignment.js b/Userland/Libraries/LibJS/Tests/non-writable-assignment.js
new file mode 100644
index 0000000000..2674cf6221
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/non-writable-assignment.js
@@ -0,0 +1,12 @@
+test("normal mode", () => {
+    expect(() => {
+        NaN = 5; // NaN is a non-writable global variable
+    }).not.toThrow();
+});
+
+test("strict mode", () => {
+    expect(() => {
+        "use strict";
+        NaN = 5; // NaN is a non-writable global variable
+    }).toThrowWithMessage(TypeError, "Cannot write to non-writable property 'NaN'");
+});