feat: Add `Deno.exitCode` API (#23609)

This commits adds the ability to set a would-be exit code 
for the Deno process without forcing an immediate exit, 
through the new `Deno.exitCode` API.

- **Implements `Deno.exitCode` getter and setter**: Adds support for
setting
and retrieving a would-be exit code via `Deno.exitCode`.
This allows for asynchronous cleanup before process termination 
without immediately exiting.
- **Ensures type safety**: The setter for `Deno.exitCode` validates that
the provided value is a number, throwing a TypeError if not, to ensure
that
only valid exit codes are set.

Closes to #23605

---------

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

2 files changed, 28 insertions, 1 deletions

diff --git a/runtime/js/30_os.js b/runtime/js/30_os.js
index 8948cf1ad..866fad287 100644
--- a/runtime/js/30_os.js
+++ b/runtime/js/30_os.js
@@ -7,6 +7,7 @@ import {
   op_exec_path,
   op_exit,
   op_get_env,
+  op_get_exit_code,
   op_gid,
   op_hostname,
   op_loadavg,
@@ -21,7 +22,9 @@ import {
 const {
   Error,
   FunctionPrototypeBind,
+  NumberParseInt,
   SymbolFor,
+  TypeError,
 } = primordials;
 
 import { Event, EventTarget } from "ext:deno_web/02_event.js";
@@ -75,7 +78,7 @@ function exit(code) {
   if (typeof code === "number") {
     op_set_exit_code(code);
   } else {
-    code = 0;
+    code = op_get_exit_code();
   }
 
   // Dispatches `unload` only when it's not dispatched yet.
@@ -94,6 +97,20 @@ function exit(code) {
   throw new Error("Code not reachable");
 }
 
+function getExitCode() {
+  return op_get_exit_code();
+}
+
+function setExitCode(value) {
+  const code = NumberParseInt(value, 10);
+  if (typeof code !== "number") {
+    throw new TypeError(
+      `Exit code must be a number, got: ${code} (${typeof code}).`,
+    );
+  }
+  op_set_exit_code(code);
+}
+
 function setEnv(key, value) {
   op_set_env(key, value);
 }
@@ -126,12 +143,14 @@ export {
   env,
   execPath,
   exit,
+  getExitCode,
   gid,
   hostname,
   loadavg,
   networkInterfaces,
   osRelease,
   osUptime,
+  setExitCode,
   setExitHandler,
   systemMemoryInfo,
   uid,
diff --git a/runtime/js/99_main.js b/runtime/js/99_main.js
index 3fa9fc41b..4f949b214 100644
--- a/runtime/js/99_main.js
+++ b/runtime/js/99_main.js
@@ -674,6 +674,14 @@ ObjectDefineProperties(finalDenoNs, {
       return internals.future ? undefined : customInspect;
     },
   },
+  exitCode: {
+    get() {
+      return os.getExitCode();
+    },
+    set(value) {
+      os.setExitCode(value);
+    },
+  },
 });
 
 const {