error-ex

0.3.1 • Public • Published

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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.
    • Values are functions that are passed the property named by key as the first argument and the .stack, split into an array of lines, as the second argument
    • Functions that return falsey values are simply skipped
    • Stack is passed as to allow direct stack message modification, if needed

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: 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 an anonymous function 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 an anonymous function 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.

Package Sidebar

Install

npm i error-ex@0.3.1

Version

0.3.1

License

MIT

Last publish

Collaborators

  • qix
  • sindresorhus