timers: be more defensive with intervals

It's possible for user-code to flip an existing timeout to
be an interval during its execution, in which case the
current code would crash due to start being undefined. Fix
this by providing a default start value within rearm.

PR-URL: https://github.com/nodejs/node/pull/18579
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

1 files changed, 12 insertions, 0 deletions

diff --git a/test/parallel/test-timers-timeout-to-interval.js b/test/parallel/test-timers-timeout-to-interval.js
new file mode 100644
index 0000000000..6952f2231a
--- /dev/null
+++ b/test/parallel/test-timers-timeout-to-interval.js
@@ -0,0 +1,12 @@
+'use strict';
+const common = require('../common');
+
+// This isn't officially supported but nonetheless is something that is
+// currently possible and as such it shouldn't cause the process to crash
+
+const t = setTimeout(common.mustCall(() => {
+  if (t._repeat) {
+    clearInterval(t);
+  }
+  t._repeat = true;
+}, 2), 1);