Address winston#1338 (updates from #59)

README.md

@@ -279,8 +279,9 @@ console.log(info);
 
 ### Errors
 
-The `errors` format allows you to pass in an instance of a JavaScript `Error` directly to the logger.
-It allows you to specify whether not to include the stack-trace.
+The `errors` format allows you to pass in an instance of a JavaScript `Error`
+directly to the logger. It allows you to specify whether not to include the
+stack-trace.
 
 ```js
 const { format } = require('logform');
@@ -304,6 +305,32 @@ console.log(info);
 //     at REPLServer.Interface._line (readline.js:631:8)
 ```
 
+It will also handle `{ message }` properties as `Error` instances:
+
+```js
+const { format } = require('logform');
+const { errors } = format;
+
+const errorsFormat = errors({ stack: true })
+
+const info = errorsFormat.transform({
+  message: new Error('Oh no!')
+});
+
+console.log(info);
+// Error: Oh no!
+//     at repl:1:13
+//     at ContextifyScript.Script.runInThisContext (vm.js:50:33)
+//     at REPLServer.defaultEval (repl.js:240:29)
+//     at bound (domain.js:301:14)
+//     at REPLServer.runBound [as eval] (domain.js:314:12)
+//     at REPLServer.onLine (repl.js:468:10)
+//     at emitOne (events.js:121:20)
+//     at REPLServer.emit (events.js:211:7)
+//     at REPLServer.Interface._onLine (readline.js:282:10)
+//     at REPLServer.Interface._line (readline.js:631:8)
+```
+
 ### JSON
 
 The `json` format uses `fast-safe-stringify` to finalize the message.

errors.js

@@ -2,7 +2,7 @@
 'use strict';
 
 const format = require('./format');
-const { MESSAGE } = require('triple-beam');
+const { LEVEL, MESSAGE } = require('triple-beam');
 
 /*
  * function errors (info)
@@ -11,15 +11,29 @@ const { MESSAGE } = require('triple-beam');
  *
  * Optionally, the Error's `stack` property can also be appended to the `info` object.
  */
-module.exports = format((info, opts) => {
-  if (!(info.message instanceof Error)) return info;
+module.exports = format((einfo, { stack }) => {
+  if (einfo instanceof Error) {
+    const info = Object.assign({}, einfo, {
+      level: einfo.level,
+      [LEVEL]: einfo[LEVEL] || einfo.level,
+      message: einfo.message,
+      [MESSAGE]: einfo[MESSAGE] || einfo.message
+    });
 
-  const err = info.message;
+    if (stack) info.stack = einfo.stack;
+    return info;
+  }
 
-  info.message = err.message;
-  info[MESSAGE] = err.message;
+  if (!(einfo.message instanceof Error)) return einfo;
 
-  if (opts.stack) info.stack = err.stack;
+  // Assign all enumerable properties and the
+  // message property from the error provided.
+  Object.assign(einfo, einfo.message);
+  const err = einfo.message;
+  einfo.message = err.message;
+  einfo[MESSAGE] = err.message;
 
-  return info;
+  // Assign the stack if requested.
+  if (stack) einfo.stack = err.stack;
+  return einfo;
 });