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: nodejs/help#1729 PR-URL: #25621 Reviewed-By: Luigi Pinca <luigipinca@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Matheus Marchini <mat@mmarchini.me>

Author: addaleax

lib/events.js

@@ -173,9 +173,18 @@ 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
  }

test/parallel/test-event-emitter-errors.js

@@ -1,6 +1,7 @@
 'use strict';
 const common = require('../common');
 const EventEmitter = require('events');
+const util = require('util');
 
 const EE = new EventEmitter();
 
@@ -9,12 +10,24 @@ common.expectsError(
  {
  code: 'ERR_UNHANDLED_ERROR',
  type: Error,
- message: 'Unhandled error. (Accepts a string)'
+ message: "Unhandled error. ('Accepts a string')"
  }
 );
 
 common.expectsError(
  () => EE.emit('error', { message: 'Error!' }),
+ {
+ code: 'ERR_UNHANDLED_ERROR',
+ type: Error,
+ message: "Unhandled error. ({ message: 'Error!' })"
+ }
+);
+
+common.expectsError(
+ () => EE.emit('error', {
+ message: 'Error!',
+ [util.inspect.custom]() { throw new Error(); }
+ }),
  {
  code: 'ERR_UNHANDLED_ERROR',
  type: Error,