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1# node-error-ex [![Travis-CI.org Build Status](https://img.shields.io/travis/Qix-/node-error-ex.svg?style=flat-square)](https://travis-ci.org/Qix-/node-error-ex) [![Coveralls.io Coverage Rating](https://img.shields.io/coveralls/Qix-/node-error-ex.svg?style=flat-square)](https://coveralls.io/r/Qix-/node-error-ex)
2> Easily subclass and customize new Error types
3
4## Examples
5To include in your project:
6```javascript
7var errorEx = require('error-ex');
8```
9
10To create an error message type with a specific name (note, that `ErrorFn.name`
11will not reflect this):
12```javascript
13var JSONError = errorEx('JSONError');
14
15var err = new JSONError('error');
16err.name; //-> JSONError
17throw err; //-> JSONError: error
18```
19
20To add a stack line:
21```javascript
22var JSONError = errorEx('JSONError', {fileName: errorEx.line('in %s')});
23
24var err = new JSONError('error')
25err.fileName = '/a/b/c/foo.json';
26throw err; //-> (line 2)-> in /a/b/c/foo.json
27```
28
29To append to the error message:
30```javascript
31var JSONError = errorEx('JSONError', {fileName: errorEx.append('in %s')});
32
33var err = new JSONError('error');
34err.fileName = '/a/b/c/foo.json';
35throw err; //-> JSONError: error in /a/b/c/foo.json
36```
37
38## API
39
40#### `errorEx([name], [properties])`
41Creates a new ErrorEx error type
42
43- `name`: the name of the new type (appears in the error message upon throw;
44 defaults to `Error.name`)
45- `properties`: if supplied, used as a key/value dictionary of properties to
46 use when building up the stack message. Keys are property names that are
47 looked up on the error message, and then passed to function values.
48 - `line`: if specified and is a function, return value is added as a stack
49 entry (error-ex will indent for you). Passed the property value given
50 the key.
51 - `stack`: if specified and is a function, passed the value of the property
52 using the key, and the raw stack lines as a second argument. Takes no
53 return value (but the stack can be modified directly).
54 - `message`: if specified and is a function, return value is used as new
55 `.message` value upon get. Passed the property value of the property named
56 by key, and the existing message is passed as the second argument as an
57 array of lines (suitable for multi-line messages).
58
59Returns a constructor (Function) that can be used just like the regular Error
60constructor.
61
62```javascript
63var errorEx = require('error-ex');
64
65var BasicError = errorEx();
66
67var NamedError = errorEx('NamedError');
68
69// --
70
71var AdvancedError = errorEx('AdvancedError', {
72 foo: {
73 line: function (value, stack) {
74 if (value) {
75 return 'bar ' + value;
76 }
77 return null;
78 }
79 }
80}
81
82var err = new AdvancedError('hello, world');
83err.foo = 'baz';
84throw err;
85
86/*
87 AdvancedError: hello, world
88 bar baz
89 at tryReadme() (readme.js:20:1)
90*/
91```
92
93#### `errorEx.line(str)`
94Creates a stack line using a delimiter
95
96> This is a helper function. It is to be used in lieu of writing a value object
97> for `properties` values.
98
99- `str`: The string to create
100 - Use the delimiter `%s` to specify where in the string the value should go
101
102```javascript
103var errorEx = require('error-ex');
104
105var FileError = errorEx('FileError', {fileName: errorEx.line('in %s')});
106
107var err = new FileError('problem reading file');
108err.fileName = '/a/b/c/d/foo.js';
109throw err;
110
111/*
112 FileError: problem reading file
113 in /a/b/c/d/foo.js
114 at tryReadme() (readme.js:7:1)
115*/
116```
117
118#### `errorEx.append(str)`
119Appends to the `error.message` string
120
121> This is a helper function. It is to be used in lieu of writing a value object
122> for `properties` values.
123
124- `str`: The string to append
125 - Use the delimiter `%s` to specify where in the string the value should go
126
127```javascript
128var errorEx = require('error-ex');
129
130var SyntaxError = errorEx('SyntaxError', {fileName: errorEx.append('in %s')});
131
132var err = new SyntaxError('improper indentation');
133err.fileName = '/a/b/c/d/foo.js';
134throw err;
135
136/*
137 SyntaxError: improper indentation in /a/b/c/d/foo.js
138 at tryReadme() (readme.js:7:1)
139*/
140```
141
142## License
143Licensed under the [MIT License](http://opensource.org/licenses/MIT).
144You can find a copy of it in [LICENSE](LICENSE).
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