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About

Error handling tools:

  • Custom Error type Failure extending the Error constructor
  • Linux/Windows standard error codes and their description
  • Error lookup: retrieve description associated to status code (or other code)
  • GoLang style error handling: return value instead of throwing
  • Rust style error handling: match Result<T, E> pattern

📦 Scoped @xan105 packages are for my own personal use but feel free to use them.

Example

import { Failure } from "@xan105/error";

if (something)
  throw new Failure("my super error message", "ERR_CODE");

Output:

Failure [ERR_CODE]: my super error message
    StackTrace...
    .............
    ............. {
  code: 'ERR_CODE'
}
  • GoLang style error
import { attempt } from "@xan105/error";
import { readFile } from "node:fs/promises";

const [ file, err ] = await attempt(readFile, [filePath]);
if(err) console.error(err); //handle error
//ignore error and set a default value
const [ json = {} ] = attempt(JSON.parse, [file]);
//skip value
const [, err] = attempt(foo, ["bar"]);

//if you prefer a node:util/promisify like syntax
import { attemptify } from "@xan105/error";
const [json] = attemptify(JSON.parse)(file);
  • Rust style error (match Result<T, E> pattern)
import { match } from "@xan105/error";
import { readFile } from "node:fs/promises";

const file = await match(readFile, [filePath], {
  Err: (err) => { console.error(err); } //handle error
});
  • Windows error lookup with shell32 API (FFI)
import { Failure, errorLookup } from "@xan105/error";

// ... Some FFI implementation code

const hr = SHQueryUserNotificationState(pquns);
if (hr < 0) throw new Failure(...errorLookup(hr));

Let's say this would fail with error 0x8000FFFF

Output:

Failure [E_UNEXPECTED]: Catastrophic failure
StackTrace...
    .............
    ............. {
  code: 'E_UNEXPECTED'
}

Install

npm install @xan105/error

API

⚠️ This module is only available as an ECMAScript module (ESM).

Named export

Failure(message: string | object, option?: string | number | object): class

Create an error with optional information.
This extends the regular Error constructor.

option default description
code none optional custom error code (see below for details)
cause none parent error if any
clean true remove unhelpful internal stack trace entries
filter none additional string[] of path(s) to filter when using clean
info none an additional object/array/string to give more details about the error

code (if any) is expected to be a string if it's an integer then the following will be used instead:

  1. ERR_UNEXPECTED
  2. ERR_INVALID_ARG
  3. ERR_ASSERTION
  4. ERR_UNSUPPORTED

if option is either a string or a number then it specifies the error code.

Output Example:

new Failure("Expecting a string !","ERR_INVALID_ARG");

Failure [ERR_INVALID_ARG]: Expecting a string !
    at file:///D:/Documents/GitHub/xan105/node-error/test/test.js:3:12
    at ModuleJob.run (node:internal/modules/esm/module_job:185:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:281:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:65:12) {
  code: 'ERR_INVALID_ARG'
}

new Failure("Expecting a string !", { code: 1, info: { foo: "bar" } });

Failure [ERR_INVALID_ARG]: Expecting a string !
    at file:///D:/Documents/GitHub/xan105/node-error/test/test.js:3:12
    at ModuleJob.run (node:internal/modules/esm/module_job:185:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:281:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:65:12) {
  code: 'ERR_INVALID_ARG',
  info: { foo: 'bar' }
}

new Failure("Expecting a string !", { clean: true });

Failure: Expecting a string !
    at file:///D:/Documents/GitHub/xan105/node-error/test/test.js:3:12
    at async Promise.all (index 0)

codes: object

A list of standard error codes with their description.
Errors are listed by their unsigned numerical value as value:number = [description: string, code: string]

{
  1: ["Operation not permitted", "EPERM"],
  2: ["No such file or directory", "ENOENT"],
  3: ["No such process", "ESRCH"],
  ...
}

Available error code range are:

  • linux

    Linux error codes 1 to 131.

  • windows

    Windows error codes 1 to 15841.

  • hresult

    HRESULT codes are most commonly encountered in COM programming. Includes common and WMI error codes.

  • ntstatus

    NTSTATUS values are mostly used like HRESULT but they have different codes.

  • win32

    Windows and hresult error codes merged together since their error code range don't overlap.
    This is also for backward compatibility with previous version of errorLookup()

They are also available under their own namespace:

import { codes } from "@xan105/error"
console.log(codes.windows);

import { windows } from "@xan105/error/codes"
console.log(windows);

Usage example:

Linux 
import { Failure, codes } from "@xan105/error"
throw new Failure(...codes.linux[2]);
/*
Failure [ENOENT]: No such file or directory
    StackTrace...
    .............
    ............. {
  code: 'ENOENT'
}
*/
import { Failure, codes } from "@xan105/error"
const [description, code] = codes.linux[1];
throw new Failure(description, { code, info: { foo: "bar" } });
/*
Failure [EPERM]: Operation not permitted,
    StackTrace...
    .............
    ............. {
  code: 'EPERM',
  info: { foo: 'bar' }
}
*/
Windows 
import { Failure, codes } from "@xan105/error"
throw new Failure(...codes.windows[2]);
/*
Failure [ERROR_FILE_NOT_FOUND]: The system cannot find the file specified
    StackTrace...
    .............
    ............. {
  code: 'ERROR_FILE_NOT_FOUND'
}
*/
import { Failure, codes } from "@xan105/error"
const [description, code] = codes.windows[1];
throw new Failure(description, { code, info: { foo: "bar" } });
/*
Failure [ERROR_INVALID_FUNCTION]: Incorrect function
    StackTrace...
    .............
    ............. {
  code: 'ERROR_INVALID_FUNCTION',
  info: { foo: 'bar' }
}
*/
Windows HRESULT

Example with error 2147749921 (0x80041021):

import { Failure, codes } from "@xan105/error"

const hr = someWin32API(); //received error -2147217375
const code = new Uint32Array([hr])[0]; //cast signed to unsigned
throw new Failure(...codes.hresult[code]);
/*
Failure [WBEM_E_INVALID_SYNTAX]: Query is syntactically not valid
    StackTrace...
    .............
    ............. {
  code: 'WBEM_E_INVALID_SYNTAX'
}
*/

errorLookup(code: number | string, range?: string): string[]

Retrieve information about an error by its numerical status code (or other code).

Return an array of string as [message: string, code?: string].

You can use it directly with Failure:

new Failure(...errorLookup(0x80041021));
new Failure(...errorLookup(2147749921));
new Failure(...errorLookup(-2147217375));
new Failure(...errorLookup("WBEM_E_INVALID_SYNTAX"));

/*
Failure [WBEM_E_INVALID_SYNTAX]: Query is syntactically not valid
    StackTrace...
    .............
    ............. {
  code: 'WBEM_E_INVALID_SYNTAX'
}
*/

See codes above for available error code range. If omitted linux is used under Linux and win32 under Windows.

attempt(fn: unknown, args?: unknown[]):Promise<unknown[]> | unknown[]

This is a try/catch wrapper to change how an error is handled.
Instead of throwing returns an error as a value similar to GoLang.

By leveraging the destructure syntax we can easily provide a default value in case of error and/or choose to completely ignore to handle any error.
And if we want to handle any error we can do so like we would with any value.

Example

import { readFile } from "node:fs/promises";
  
//read the file
const [ file, err ] = await attempt(readFile, [filePath]);
if(err) //in case of error do something;

//ignore error and set a default value
const [ json = {} ] = attempt(JSON.parse, [file]);

//skip value
const [, err] = attempt(foo, ["bar"]);

This doesn't replace try/catch it's an alternative.
It is particularly useful to avoid these patterns:

  • Using let instead of const because the variable needs to be outside of the try/catch scope.
//Instead of
let json;
try{
  json = JSON.parse(string);
} catch { /*do nothing*/ }
return json; //do something

//You could do
const [ json ] = attempt(JSON.parse,[string]);
return json; //do something
  • Nested try/catch which are sometimes unavoidable and impact readability.
//Instead of
try{
  foo();
}catch(err){
  try{
    bar();
  }catch(err){
    if (err.code === "ENOENT")
      throw new Error("It didn't work");
  }
}

//You could do
if (attempt(foo)[1] && attempt(bar)[1]?.code === "ENOENT"){
  throw new Error("It didn't work");    
}

Parameters:

  • fn: The value to resolve

If fn is a promise then this function will behave like one. eg:

//Promise
const [ file ] = await attempt(fs.Promises.readFile, [filePath]);
//Sync
const [ json ] = attempt(JSON.parse, [file]);

You can also use anonymous function (or wrap in one). eg:

const [result] = attempt( ()=> "value" );
const [result] = attempt( (x)=> x, ["value"] );
const [json] = attempt(()=> JSON.parse(string) );
const [json] = attempt(()=> JSON.stringify(JSON.parse(string)) );
  • args: Optional list of arguments to pass to fn

Return value:

Returns the result and the error together as an array as [result, error].
If there is an error result will be undefined.
Otherwise error will be undefined.

💡 undefined is used to represent the lack/nonexistence of value because destructuring default value assignment triggers only with undefined.

Usage example with node:util/promisify:

import { promisify } from "node:util";
import { execFile } from "node:child_process";
import { attempt, Failure } from "@xan105/error";

const [ ps, err ] = await attempt(promisify(execFile), ["pwsh", [
  "-NoProfile", 
  "-NoLogo", 
  "-Command", 
  "$PSVersionTable.PSVersion.ToString()"
], { windowsHide: true }]);

if (err || ps.stderr) throw new Failure(err?.stderr || ps.stderr, "ERR_POWERSHELL");
console.log(ps.stdout);

Special case

Loosing "this" context

⚠️ NB: If you get an error like:

TypeError: x called on non-object
TypeError: Illegal invocation

This is most likely because what you are invoking lost its this context. You need to bind it to its constructor or use an arrow function.

Promise static methods such as .all(), .any(), .allSettled() , etc is a good example of this:

const promise1 = new Promise((resolve) => setTimeout(resolve, 100, 'quick'));
const promise2 = new Promise((resolve) => setTimeout(resolve, 500, 'slow'));
const promises = [promise1, promise2];

//This will succeed
const [ result, error ] = await attempt(()=> Promise.any(promises));

//This will fail with a TypeError
const [ result, error ] = await attempt(Promise.any, [promises]);
/*
[
  undefined,
  TypeError: Promise.any called on non-object
      at any (<anonymous>)
      StackTrace...
]
*/

//This will succeed
const [ result, error ] = await attempt(Promise.any.bind(Promise), [promises]);
Computed properties (Getter/Setter)

The actual function behind the Getter/Setter will be called when that property is looked up. Therefore if there was any error it would throw before attempt() could catch it.

class Foo {
  constructor(){}
  
  get bar(){
    throw new Error("error");
  }
}

const foo = new Foo();
const [, err] = attempt(foo.bar);

To catch it you need to pass the actual function behind the Getter/Setter.

class Foo {
  constructor(){}
  
  get bar(){
    throw new Error("error");
  }
}

const foo = new Foo();
const descriptor = Object.getOwnPropertyDescriptor(Object.getPrototypeOf(foo), "bar");
const [, err] = attempt(descriptor?.["get"]);

attemptify(fn: unknown): (...args: unknown[]) => Promise<unknown[]> | unknown[]

node:util/promisify style syntax for attempt():

function double(i){
  return i * 2;
}

//Instead of
const j = attempt(double, [2]);

//You can use
const j = attemptify(double)(2);

This is a simple wrapper to attempt().

match(fn: unknown, args: unknown[], cb?: { Ok?: function, Err?: function }):Promise<unknown> | unknown

This is a try/catch wrapper to change how an error is handled.
Similar to the Rust match Result<T, E> pattern:

Success is handled by the Ok() function and failure by the Err() function respectively.

const greetings = (name) => `hello ${name}`;

const message = match(greetings, ["Xan"], {
  Ok: (value) => value,
  Err: (err) => { console.log(err) }
});

The Ok() function is expected to return the value the match() function shall return for value assignment.
💡 Ok() and Err() can both be omitted.

const greetings = (name) => `hello ${name}`;

const message = match(greetings, ["Xan"], {
  Err: (err) => { console.log(err) }
});

If fn is a promise then this function will behave like one:

//Promise
const file = await match(fs.Promises.readFile, [filePath]);
//Sync
const json = match(JSON.parse, [file]);

In case of error, If Err() returns a value it will be used for value assignment.
Use this to ignore an error and set a default value:

const json = match(JSON.parse, [file], {
  Err: ()=> { return {} }
});

Special case

⚠️ This function is similar to the above export attempt() and therefore inherits the same remarks (see above).

About

Error handling tools

Topics

nodejs match fail error failure attempt errorcode errorlookup

Resources

Readme

License

MIT license
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