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doc: update System Errors documentation
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Simplify text. Add explanation that `code` is the most stable way to
identify an error, in contrast with `message` which is subject to change
between patch-level versions of Node.js. Synchronize list of properties
with text. Order properties alphabetically.

PR-URL: #24090
Fixes: #23975
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
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Trott authored and MylesBorins committed Nov 29, 2018
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96 changes: 51 additions & 45 deletions doc/api/errors.md
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Expand Up @@ -441,86 +441,93 @@ checks or `abort()` calls in the C++ layer.

## System Errors

System errors are generated when exceptions occur within the Node.js
runtime environment. Typically, these are operational errors that occur
when an application violates an operating system constraint such as attempting
to read a file that does not exist or when the user does not have sufficient
permissions.
Node.js generates system errors when exceptions occur within its runtime
environment. These usually occur when an application violates an operating
system constraint. For example, a system error will occur if an application
attempts to read a file that does not exist.

System errors are typically generated at the syscall level: an exhaustive list
of error codes and their meanings is available by running `man 2 intro` or
`man 3 errno` on most Unices; or [online][].
System errors are usually generated at the syscall level. For a comprehensive
list, see the [`errno`(3) man page][].

In Node.js, system errors are represented as augmented `Error` objects with
added properties.
In Node.js, system errors are `Error` objects with extra properties.

### Class: SystemError

#### error.info
* `address` {string} If present, the address to which a network connection
failed
* `code` {string} The string error code
* `dest` {string} If present, the file path destination when reporting a file
system error
* `errno` {number|string} The system-provided error number
* `info` {Object} If present, extra details about the error condition
* `message` {string} A system-provided human-readable description of the error
* `path` {string} If present, the file path when reporting a file system error
* `port` {number} If present, the network connection port that is not available
* `syscall` {string} The name of the system call that triggered the error

`SystemError` instances may have an additional `info` property whose
value is an object with additional details about the error conditions.
#### error.address

The following properties are provided:
* {string}

* `code` {string} The string error code
* `errno` {number} The system-provided error number
* `message` {string} A system-provided human readable description of the error
* `syscall` {string} The name of the system call that triggered the error
* `path` {Buffer} When reporting a file system error, the `path` will identify
the file path.
* `dest` {Buffer} When reporting a file system error, the `dest` will identify
the file path destination (if any).
If present, `error.address` is a string describing the address to which a
network connection failed.

#### error.code

* {string}

The `error.code` property is a string representing the error code, which is
typically `E` followed by a sequence of capital letters.
The `error.code` property is a string representing the error code.

#### error.dest

* {string}

If present, `error.dest` is the file path destination when reporting a file
system error.

#### error.errno

* {string|number}

The `error.errno` property is a number or a string.
The number is a **negative** value which corresponds to the error code defined
in [`libuv Error handling`]. See `uv-errno.h` header file
(`deps/uv/include/uv-errno.h` in the Node.js source tree) for details. In case
The `error.errno` property is a number or a string. If it is a number, it is a negative value which corresponds to the error code defined in
[`libuv Error handling`]. See the libuv `errno.h` header file
(`deps/uv/include/uv/errno.h` in the Node.js source tree) for details. In case
of a string, it is the same as `error.code`.

#### error.syscall
#### error.info

* {string}
* {Object}

The `error.syscall` property is a string describing the [syscall][] that failed.
If present, `error.info` is an object with details about the error condition.

#### error.path
#### error.message

* {string}

When present (e.g. in `fs` or `child_process`), the `error.path` property is a
string containing a relevant invalid pathname.
`error.message` is a system-provided human-readable description of the error.

#### error.address
#### error.path

* {string}

When present (e.g. in `net` or `dgram`), the `error.address` property is a
string describing the address to which the connection failed.
If present, `error.path` is a string containing a relevant invalid pathname.

#### error.port

* {number}

When present (e.g. in `net` or `dgram`), the `error.port` property is a number
representing the connection's port that is not available.
If present, `error.port` is the network connection port that is not available.

#### error.syscall

* {string}

The `error.syscall` property is a string describing the [syscall][] that failed.

### Common System Errors

This list is **not exhaustive**, but enumerates many of the common system
errors encountered when writing a Node.js program. An exhaustive list may be
found [here][online].
This is a list of system errors commonly-encountered when writing a Node.js
program. For a comprehensive list, see the [`errno`(3) man page][].

- `EACCES` (Permission denied): An attempt was made to access a file in a way
forbidden by its file access permissions.
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[`ERR_INVALID_ARG_TYPE`]: #ERR_INVALID_ARG_TYPE
[`EventEmitter`]: events.html#events_class_eventemitter
[`fs`]: fs.html
[`fs.readdir`]: fs.html#fs_fs_readdir_path_options_callback
[`errno`(3) man page]: http://man7.org/linux/man-pages/man3/errno.3.html
[`fs.readFileSync`]: fs.html#fs_fs_readfilesync_path_options
[`fs.readdir`]: fs.html#fs_fs_readdir_path_options_callback
[`fs.symlink()`]: fs.html#fs_fs_symlink_target_path_type_callback
[`fs.symlinkSync()`]: fs.html#fs_fs_symlinksync_target_path_type
[`fs.unlink`]: fs.html#fs_fs_unlink_path_callback
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[domains]: domain.html
[event emitter-based]: events.html#events_class_eventemitter
[file descriptors]: https://en.wikipedia.org/wiki/File_descriptor
[ICU]: intl.html#intl_internationalization_support
[online]: http://man7.org/linux/man-pages/man3/errno.3.html
[stream-based]: stream.html
[syscall]: http://man7.org/linux/man-pages/man2/syscalls.2.html
[try-catch]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch
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