fix(runtime): fix recursive dispatches of unload event (#9207)

cli/tests/078_unload_on_exit.ts

@@ -1,4 +1,9 @@
 window.onunload = () => {
   console.log("onunload is called");
+  // This second exit call doesn't trigger unload event,
+  // and therefore actually stops the process.
+  Deno.exit(1);
+  console.log("This doesn't show up in console");
 };
+// This exit call triggers the above unload event handler.
 Deno.exit(0);

cli/tests/integration_tests.rs

@@ -2665,6 +2665,7 @@ itest!(_077_fetch_empty {
 itest!(_078_unload_on_exit {
   args: "run 078_unload_on_exit.ts",
   output: "078_unload_on_exit.ts.out",
+  exit_code: 1,
 });
 
 itest!(_079_location_authentication {

runtime/js/30_os.js

@@ -24,9 +24,12 @@
   }
 
   function exit(code = 0) {
+    // Dispatches `unload` only when it's not dispatched yet.
+    if (!window[Symbol.for("isUnloadDispatched")]) {
       // Invokes the `unload` hooks before exiting
       // ref: https://github.com/denoland/deno/issues/3603
       window.dispatchEvent(new Event("unload"));
+    }
     core.jsonOpSync("op_exit", { code });
     throw new Error("Code not reachable");
   }

runtime/js/99_main.js

@@ -305,6 +305,15 @@ delete Object.prototype.__proto__;
     defineEventHandler(window, "load", null);
     defineEventHandler(window, "unload", null);
 
+    const isUnloadDispatched = Symbol.for("isUnloadDispatched");
+    // Stores the flag for checking whether unload is dispatched or not.
+    // This prevents the recursive dispatches of unload events.
+    // See https://github.com/denoland/deno/issues/9201.
+    window[isUnloadDispatched] = false;
+    window.addEventListener("unload", () => {
+      window[isUnloadDispatched] = true;
+    });
+
     runtimeStart(runtimeOptions);
     const {
       args,