events: show inspected error in uncaught 'error' message

If there is no handler for `.emit('error', value)` and `value`
is not an `Error` object, we currently just call `.toString()`
on it.

Almost always, using `util.inspect()` provides better information
for diagnostic purposes, so prefer to use that instead.

Refs: https://github.com/nodejs/help/issues/1729

PR-URL: https://github.com/nodejs/node/pull/25621
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/events.js b/lib/events.js
index 10cec4bd69..fab8652ebf 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -172,9 +172,18 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
       // up in Node's output if this results in an unhandled exception.
       throw er; // Unhandled 'error' event
     }
+
+    let stringifiedEr;
+    const { inspect } = require('internal/util/inspect');
+    try {
+      stringifiedEr = inspect(er);
+    } catch {
+      stringifiedEr = er;
+    }
+
     // At least give some kind of context to the user
     const errors = lazyErrors();
-    const err = new errors.ERR_UNHANDLED_ERROR(er);
+    const err = new errors.ERR_UNHANDLED_ERROR(stringifiedEr);
     err.context = er;
     throw err; // Unhandled 'error' event
   }