node-error-ex

Easily subclass and customize new Error types

Examples

To include in your project:
javascript var errorEx = require('error-ex');

To create an error message type with a specific name (note, that ErrorFn.name
will not reflect this):
```javascript
var JSONError = errorEx('JSONError');

var err = new JSONError('error');
err.name; //-> JSONError
throw err; //-> JSONError: error
```

To add a stack line:
```javascript
var JSONError = errorEx('JSONError', {fileName: errorEx.line('in %s')});

var err = new JSONError('error')
err.fileName = '/a/b/c/foo.json';
throw err; //-> (line 2)-> in /a/b/c/foo.json
```

To append to the error message:
```javascript
var JSONError = errorEx('JSONError', {fileName: errorEx.append('in %s')});

var err = new JSONError('error');
err.fileName = '/a/b/c/foo.json';
throw err; //-> JSONError: error in /a/b/c/foo.json
```

API

errorEx([name], [properties])

Creates a new ErrorEx error type

• name: the name of the new type (appears in the error message upon throw;
  defaults to Error.name)
• properties: if supplied, used as a key/value dictionary of properties to
  use when building up the stack message. Keys are property names that are
  looked up on the error message, and then passed to function values.
  • line: if specified and is a function, return value is added as a stack
    entry (error-ex will indent for you). Passed the property value given
    the key.
• stack: if specified and is a function, passed the value of the property
  using the key, and the raw stack lines as a second argument. Takes no
  return value (but the stack can be modified directly).
• message: if specified and is a function, return value is used as new
  .message value upon get. Passed the property value of the property named
  by key, and the existing message is passed as the second argument as an
  array of lines (suitable for multi-line messages).

Returns a constructor (Function) that can be used just like the regular Error
constructor.

var errorEx = require('error-ex');

var BasicError = errorEx();

var NamedError = errorEx('NamedError');

// --

var AdvancedError = errorEx('AdvancedError', {
	foo: {
		line: function (value, stack) {
			if (value) {
				return 'bar ' + value;
			}
			return null;
		}
	}
}

var err = new AdvancedError('hello, world');
err.foo = 'baz';
throw err;

/*
	AdvancedError: hello, world
	    bar baz
	    at tryReadme() (readme.js:20:1)
*/

errorEx.line(str)

Creates a stack line using a delimiter

This is a helper function. It is to be used in lieu of writing a value object
for properties values.

• str: The string to create
• Use the delimiter %s to specify where in the string the value should go

var errorEx = require('error-ex');

var FileError = errorEx('FileError', {fileName: errorEx.line('in %s')});

var err = new FileError('problem reading file');
err.fileName = '/a/b/c/d/foo.js';
throw err;

/*
	FileError: problem reading file
	    in /a/b/c/d/foo.js
	    at tryReadme() (readme.js:7:1)
*/

errorEx.append(str)

Appends to the error.message string

This is a helper function. It is to be used in lieu of writing a value object
for properties values.

• str: The string to append
• Use the delimiter %s to specify where in the string the value should go

var errorEx = require('error-ex');

var SyntaxError = errorEx('SyntaxError', {fileName: errorEx.append('in %s')});

var err = new SyntaxError('improper indentation');
err.fileName = '/a/b/c/d/foo.js';
throw err;

/*
	SyntaxError: improper indentation in /a/b/c/d/foo.js
	    at tryReadme() (readme.js:7:1)
*/

License

Licensed under the MIT License.
You can find a copy of it in LICENSE.