standard-error

StandardError.js
================
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StandardError.js is a tiny JavaScript library that simplifies creating
subclasses of Error for custom error classes with the correct name and
stack property. Saves you from writing a few lines of boilerplate.

$3

- Create custom error classes and add new behavior to them while keeping the
standard Error behavior in tact.
- Add extra properties to the error by just passing in an object.
- StandardError.js sets the error's stack trace correctly, even if your
error class subclasses/inherits from StandardError.
Just inheriting from Error with Object.create breaks the stack trace.
- Every StandardError instance is also an instance of Error.
- Serializes all expected properties when passing it to JSON.stringify.
Did you know that the default Error object serializes to an empty object
({})?
- Works both in Node.js and browsers and sets the stack trace via
Error.captureStackTrace where available.

Installing
----------
``
npm install standard-error
`


Using
-----
Just require StandardError.js and either use it directly or inherit from it for
your custom error class.

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Like Error, StandardError takes a message argument, but in addition to that,
you may give it an object with other properties to be set:

`javascript
var StandardError = require("standard-error")
throw new StandardError("Not Found", {code: 404})
`

The thrown instance of StandardError will then have both the message and the
code property.
It'll also also have a name property set to "StandardError".

You can skip the explicit message argument and give everything as an
object of properties:

`javascript
new StandardError({message: "Not Found", code: 404})
`

Note: All properties besides stack will be enumerable for easier
serialization with JSON.stringify. That includes the name property which
will be set from the constructor's name (defaults to "StandardError").

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The real benefit of StandardError.js comes from subclassing it to create new
error classes and adding custom behavior to them.

Let's create an HttpError that we can instantiate with the HTTP status code
(new HttpError(404)) and have it set the message automatically based on that:

`javascript
var Http = require("http")
var StandardError = require("standard-error")

function HttpError(code, msg) {
StandardError.call(this, msg || Http.STATUS_CODES[code], {code: code})
}

HttpError.prototype = Object.create(StandardError.prototype, {
constructor: {value: HttpError, configurable: true, writable: true}
})
`

Note that you must set the constructor property like in the above
example. First, that's the proper way to subclass in JavaScript and second,
StandardError.js depends on that to know which functions to skip in the stack
trace.

#### Name

StandardError.js finds out the name (err.name) of your subclassed error from
its constructor function. However, if you minify your code, you can also set or
change it explicitly:

`javascript
ChildError.prototype.name = "FallacyError"
`

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Now that you've inherited, you can, for example, customize stringifying by
overwriting toString on your subclass. To get new HttpError(404) to print
itself as 404 Not Found:

`javascript
HttpError.prototype.toString = function() {
return this.code + " " + this.message
}
`

License
-------
StandardError.js is released under a Lesser GNU Affero General Public License, which
in summary means:

- You can use this program for no cost.
- You can use this program for both personal and commercial reasons.
- You do not have to share your own program's code which uses this program.
- You have to share modifications (e.g. bug-fixes) you've made to this
program.

For more convoluted language, see the LICENSE` file.

About
-----
Andri Möll typed this and the code.
Monday Calendar supported the engineering work.

If you find StandardError.js needs improving, please don't hesitate to type to
me now at [andri@dot.ee][email] or [create an issue online][issues].

[email]: mailto:andri@dot.ee
[issues]: https://github.com/moll/js-standard-error/issues