node-error-ex

Easily subclass and customize new Error types

Examples

To include in your project:

1var errorEx = require('error-ex');

To create an error message type with a specific name (note, that ErrorFn.name will not reflect this):

1var JSONError = errorEx('JSONError');
2
3var err = new JSONError('error');
4err.name; //-> JSONError
5throw err; //-> JSONError: error

To add a stack line:

1var JSONError = errorEx('JSONError', {fileName: errorEx.line('in %s')});
2
3var err = new JSONError('error')
4err.fileName = '/a/b/c/foo.json';
5throw err; //-> (line 2)-> in /a/b/c/foo.json

To append to the error message:

1var JSONError = errorEx('JSONError', {fileName: errorEx.append('in %s')});
2
3var err = new JSONError('error');
4err.fileName = '/a/b/c/foo.json';
5throw 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.

1var errorEx = require('error-ex');
2
3var BasicError = errorEx();
4
5var NamedError = errorEx('NamedError');
6
7// --
8
9var AdvancedError = errorEx('AdvancedError', {
10	foo: {
11		line: function (value, stack) {
12			if (value) {
13				return 'bar ' + value;
14			}
15			return null;
16		}
17	}
18})
19
20var err = new AdvancedError('hello, world');
21err.foo = 'baz';
22throw err;
23
24/*
25	AdvancedError: hello, world
26	    bar baz
27	    at tryReadme() (readme.js:20:1)
28*/

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

1var errorEx = require('error-ex');
2
3var FileError = errorEx('FileError', {fileName: errorEx.line('in %s')});
4
5var err = new FileError('problem reading file');
6err.fileName = '/a/b/c/d/foo.js';
7throw err;
8
9/*
10	FileError: problem reading file
11	    in /a/b/c/d/foo.js
12	    at tryReadme() (readme.js:7:1)
13*/

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

1var errorEx = require('error-ex');
2
3var SyntaxError = errorEx('SyntaxError', {fileName: errorEx.append('in %s')});
4
5var err = new SyntaxError('improper indentation');
6err.fileName = '/a/b/c/d/foo.js';
7throw err;
8
9/*
10	SyntaxError: improper indentation in /a/b/c/d/foo.js
11	    at tryReadme() (readme.js:7:1)
12*/

License

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