fix(runtime): Declare `Window.self` and `DedicatedWorkerGlobalScope.name` with `util.writable()` (#12378)

`Window`'s `self` property and `DedicatedWorkerGlobalScope`'s `name`
property are defined as Web IDL read-only attributes with the
`[Replaceable]` extended attribute, meaning that their setter will
redefine the property as a data property with the set value, rather than
changing some internal state. Deno currently defines them as read-only
data properties instead.

Given that Web IDL requires all attributes to be accessor properties
rather than data properties, but Deno exposes almost all of those
properties as either read-only or writable data properties, it makes
sense to expose `[Replaceable]` properties as writable as well – as is
already the case with `WindowOrWorkerGlobalScope`'s `performance`
property.

1 files changed, 21 insertions, 0 deletions

diff --git a/cli/tests/testdata/replace_self.js b/cli/tests/testdata/replace_self.js
new file mode 100644
index 000000000..cfd473cd3
--- /dev/null
+++ b/cli/tests/testdata/replace_self.js
@@ -0,0 +1,21 @@
+// Test that setting `self` in the main thread to some other value doesn't break
+// the world, in particular for events fired on the global scope.
+
+// deno-lint-ignore no-global-assign
+self = null;
+
+addEventListener("load", () => {
+  console.log("load event (event listener)");
+});
+
+addEventListener("unload", () => {
+  console.log("unload event (event listener)");
+});
+
+globalThis.onload = () => {
+  console.log("load event (event handler)");
+};
+
+globalThis.onunload = () => {
+  console.log("unload event (event handler)");
+};