node-error-ex 
Easily subclass and customize new Error types
Examples
To include in your project:
var errorEx = require('error-ex');
To create an error message type with a specific name (note, that ErrorFn.name
will not reflect this):
var JSONError = errorEx('JSONError');
var err = new JSONError('error');
err.name; //-> JSONError
throw err; //-> JSONError: error
To add a stack line:
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:
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.
