fix: Allow cleaning the exit handler inside the handler itself

src/index.ts

@@ -104,7 +104,7 @@ class Emitter {
     }
     this.emitted[ev] = true
     let ret: boolean = false
-    for (const fn of this.listeners[ev]) {
+    for (const fn of [...this.listeners[ev]]) {
       ret = fn(code, signal) === true || ret
     }
     if (ev === 'exit') {

test/fixtures/remove-handler.js

@@ -0,0 +1,10 @@
+const { onExit } = require('../../')
+
+const cleanup = onExit(function () {
+  console.log('one')
+  cleanup()
+})
+
+onExit(function () {
+  console.log('two')
+})

test/remove-handler.js

@@ -0,0 +1,14 @@
+const { execFile } = require('node:child_process')
+const { resolve } = require('node:path')
+const { promisify } = require('node:util')
+const t = require('tap')
+
+const pExecFile = promisify(execFile)
+
+const fixture = resolve(__dirname, 'fixtures/remove-handler.js')
+
+t.test('Cleanup function can be called inside the exit handler', async t => {
+  const {stderr, stdout} = await pExecFile(process.execPath, [fixture])
+  t.equal(stderr, '')
+  t.equal(stdout, 'one\ntwo\n')
+})