error-extender-1.0.2

Simplifies creation of custom Error classes for Node.js!

...which then produces stack with appended stacks of supplied cause _(very much like in Java)_!

``javascript
const extendError = require('error-extender');

const CustomError = extendError('CustomError');

const rootCause = new Error('the root cause');

console.log(new CustomError({ message: 'An error has occurred.', cause: rootCause }));
`

Shall output:

`
CustomError: An error has occurred.
at Object. (/opt/app/index.js:7:13)
at Module._compile (internal/modules/cjs/loader.js:702:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
at Module.load (internal/modules/cjs/loader.js:612:32)
at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
at Function.Module._load (internal/modules/cjs/loader.js:543:3)
at Function.Module.runMain (internal/modules/cjs/loader.js:744:10)
at startup (internal/bootstrap/node.js:240:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:564:3)
Caused by: Error: the root cause
at Object. (/opt/app/index.js:5:19)
at Module._compile (internal/modules/cjs/loader.js:702:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
at Module.load (internal/modules/cjs/loader.js:612:32)
at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
at Function.Module._load (internal/modules/cjs/loader.js:543:3)
at Function.Module.runMain (internal/modules/cjs/loader.js:744:10)
at startup (internal/bootstrap/node.js:240:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:564:3)
`

$3

Oh, by the way, 100% test coverage. See for yourself (via npm test)!

Features

$3

It's quite simple! See below:

`javascript
const extendError = require('error-extender');

const AppError = extendError('AppError'); // extends Error (default)
`

Or... A bit more complex using the second argument _(options)_:

`javascript
const extendError = require('error-extender');

const AppError = extendError('AppError', {
defaultMessage: 'An unhandled error has occurred.',
defaultData: { status: 503, message: 'An unhandled error has occurred.' }
});

const ServiceError = extendError('ServiceError', {
parent: AppError, // extends AppError
defaultMessage: 'A service error has occurred.',
defaultData: { status: 500, message: 'A service error has occurred.' }
});

const DatabaseError = extendError('DatabaseError', {
parent: ServiceError, // extends ServiceError
defaultMessage: 'A service database error has occurred.',
defaultData: { message: 'A service database error has occurred.' }
});

require('assert').deepStrictEqual(
DatabaseError.defaultData, {
status: 500,
message: 'A service database error has occurred.'
});
// no error
`

Yes, defaultData merges!

#### error-extender Arguments

error-extender accepts a single object literal as second argument.

The options (object literal keys) are as follows:

| key | expected type |
| ---------------- | ------------------------------------------ |
| parent | Error.prototype _or one that extends it_ |
| defaultMessage | string |
| defaultData | any |

$3

1) Creates prototype-based Error classes (child/subclass) : _"Extended Errors"_.
1) Those _"Extended Errors"_, accepts cause (Error); very much like how it is with Java Exception.
1) Appends stack of cause to the bottom of instantiated _"Extended Errors"_ stack.
1) _"Extended Errors"_ constructor & argument _(w/ optional new)_:
1) new ExtendedError(options)
1) ExtendedError(options)

Yes, much like JavaScript's native Error, "Extended Errors" can be written/used "factory-like" (without the new keyword).

#### "Extended Errors" Arguments (constructor)

"Extended Errors" accepts a single object literal as argument:

`javascript
const extendError = require('error-extender');
const ServiceError = extendError('ServiceError');
try {
// ... something throws something
} catch (error) {
throw new ServiceError({
message: 'An error has occurred',
data: { ref: '7e9f876ca116' },
cause: error
});
}
`

The options (object literal keys) are as follows:

| key | alias | expected type |
| :-------- | :---: | ------------------- |
| message | m | string |
| data | d | any |
| cause | c | instancedof Error |

Given the alias, you may construct extended errors by:

`javascript
const extendError = require('error-extender');
const ServiceError = extendError('ServiceError');
try {
// ... something throws something
} catch (error) {
throw new ServiceError({
m: 'An error has occurred',
d: { ref: '7e9f876ca116' },
c: error
});
}
`

Note: Aliases are evaluated first; hence if you have both m and message, if m's value is truthy, then m's value will be used.

#### Instance Properties

As with Error, "Extended Errors" would have the following properties:

* name
* message
* stack

... "Extended Errors" shall have the following additiona properties:

* data - _(as set in constructor args)_
* cause - _(as set in constructor args)_

#### data merging w/ defaultData

Yes, you heard right, instance data merges with defaultData!!!

See example below:

`javascript
const extendError = require('error-extender');

const AppError = extendError('ServiceError', {
defaultData: { status: 503, message: 'An unhandled error has occurred.' }
});

const appError = new AppError({ d: { status: 401 } });

require('assert').deepStrictEqual(
appError.data, {
status: 401,
message: 'An unhandled error has occurred.'
});
// no error
`



The inspiration (thanks bluebird!):



`javascript
const Promise = require('bluebird');
// ...
const extendError = require('error-extender');
// ...
const ServiceError = extendError('ServiceError');
const ServiceStateError = extendError(
'ServiceStateError',
{ parent: ServiceError });
// ...
function aServiceFunction() {
return new Promise(
function (resolve, reject) {
// ... multiple things that may throw your
// custom "expected" errors
})
.catch(ServiceStateError, function (error) {
// ... your "common way" of handling
// ServiceStateError
// ... then propagate
})
.catch(ServiceError, function (error) {
// ... your "common generc way" of handling
// ServiceError
// ... then propagate
})
.catch(function (error) {
// ... the "catch all"
// ... then propagate
});
}
`

With JavaScript, I felt quite stifled when I was limited to:

1) Do selective/custom handling based on matching messages from throw new Error('..').
1) Return/propagate JSend-like responses to function "callers"/"users".
1) ... or whatever error possible passing/handling could be done, throughout functions and callers/users.

With error-extender with help from syntactic-sugar from bluebird`, you can improve _(or even standardize)_ your way of propagating/handling errors throughout your application.
callers.

License

$3

#### Copyright (c) 2018 Joseph Baking

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.