Gist for creating custom error objects, with inheritance, factory-function and instanceof functionality.

ErrorFactory.js

/**
 * Custom Error classes factory
 * Usage:
 * var MyError = ErrorFactory('MyError');
 * try{
 *     throw new MyError('my error text'); //or throw MyError('my error text');
 * }catch(e){
 *     if(e instanceof MyError){
 *         console.log('This is my error!');
 *     }
 * }
 */
"use strict";
define(
	['underscore'],
	function(_){
		/**
		 * Function-factory, creates custom Error classes
		 * @param  {String} name Name for new class
		 * @return {Error}       New Error class
		 */
		return function(name){
			if(name === undefined || !_.isString(name)){
				throw new Error('You must set class name');
			}

			//constructor
			function CustomError(message){
				//for using without new statement
				if(this === undefined){
					return new CustomError(message);
				}

				this.name    = name;
				this.message = message || '';
			}
			//inheritance
			CustomError.prototype = new Error();
			CustomError.prototype.constructor = CustomError;

			return CustomError;
		}
	}
);