doc: document ES2022's Error "cause" property

ide · danielleadams · commit 976093efe3d2 · 2022-07-25T21:43:38.000-04:00
ES2022 adds an `options` parameter to the `Error` constructor. If the options argument contains a property named `cause`, the property's value is assigned to a non-enumerable property named `cause` on the newly created error. The `cause` property is not referenced anywhere else in the ES2022/2023 specifications. It is for error-formatting software like `util.inspect()` to consume. The `cause` property was added in V8 9.3, which was added to Node 16.9.0. Refs: https://tc39.es/ecma262/#sec-error-message Refs: https://github.com/nodejs/node/blob/main/doc/changelogs/CHANGELOG_V16.md#error-cause PR-URL: #43830 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
diff --git a/doc/api/errors.md b/doc/api/errors.md
@@ -191,13 +191,16 @@ provide a text description of the error.
 All errors generated by Node.js, including all system and JavaScript errors,
 will either be instances of, or inherit from, the `Error` class.
 
-### `new Error(message)`
+### `new Error(message[, options])`
 
 * `message` {string}
+* `options` {Object}
+  * `cause` {any} The error that caused the newly created error.
 
 Creates a new `Error` object and sets the `error.message` property to the
 provided text message. If an object is passed as `message`, the text message
-is generated by calling `message.toString()`. The `error.stack` property will
+is generated by calling `String(message)`. If the `cause` option is provided,
+it is assigned to the `error.cause` property. The `error.stack` property will
 represent the point in the code at which `new Error()` was called. Stack traces
 are dependent on [V8's stack trace API][]. Stack traces extend only to either
 (a) the beginning of _synchronous code execution_, or (b) the number of frames
@@ -253,6 +256,49 @@ will affect any stack trace captured _after_ the value has been changed.
 If set to a non-number value, or set to a negative number, stack traces will
 not capture any frames.
 
+### `error.cause`
+
+<!-- YAML
+added: v16.9.0
+-->
+
+* {any}
+
+If present, the `error.cause` property is the underlying cause of the `Error`.
+It is used when catching an error and throwing a new one with a different
+message or code in order to still have access to the original error.
+
+The `error.cause` property is typically set by calling
+`new Error(message, { cause })`. It is not set by the constructor if the
+`cause` option is not provided.
+
+This property allows errors to be chained. When serializing `Error` objects,
+[`util.inspect()`][] recursively serializes `error.cause` if it is set.
+
+```js
+const cause = new Error('The remote HTTP server responded with a 500 status');
+const symptom = new Error('The message failed to send', { cause });
+
+console.log(symptom);
+// Prints:
+//   Error: The message failed to send
+//       at REPL2:1:17
+//       at Script.runInThisContext (node:vm:130:12)
+//       ... 7 lines matching cause stack trace ...
+//       at [_line] [as _line] (node:internal/readline/interface:886:18) {
+//     [cause]: Error: The remote HTTP server responded with a 500 status
+//         at REPL1:1:15
+//         at Script.runInThisContext (node:vm:130:12)
+//         at REPLServer.defaultEval (node:repl:574:29)
+//         at bound (node:domain:426:15)
+//         at REPLServer.runBound [as eval] (node:domain:437:12)
+//         at REPLServer.onLine (node:repl:902:10)
+//         at REPLServer.emit (node:events:549:35)
+//         at REPLServer.emit (node:domain:482:12)
+//         at [_onLine] [as _onLine] (node:internal/readline/interface:425:12)
+//         at [_line] [as _line] (node:internal/readline/interface:886:18)
+```
+
 ### `error.code`
 
 * {string}
@@ -3514,6 +3560,7 @@ The native call from `process.cpuUsage` could not be processed.
 [`subprocess.send()`]: child_process.md#subprocesssendmessage-sendhandle-options-callback
 [`url.parse()`]: url.md#urlparseurlstring-parsequerystring-slashesdenotehost
 [`util.getSystemErrorName(error.errno)`]: util.md#utilgetsystemerrornameerr
+[`util.inspect()`]: util.md#utilinspectobject-options
 [`util.parseArgs()`]: util.md#utilparseargsconfig
 [`v8.startupSnapshot.setDeserializeMainFunction()`]: v8.md#v8startupsnapshotsetdeserializemainfunctioncallback-data
 [`zlib`]: zlib.md
