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Helper for creating easily extensible and subclassable JavaScript Error classes.


Make sure you have node.js and npm installed, then run:

npm install createerror


var createError = require('createerror');

var MyError = createError({
    name: 'MyError',
    // Used when no message is handed to the constructor:
    message: 'A slightly longer description of the error'

Instances can carry extra data about the error:

try {
    throw new MyError({
        message: "The message", // Not mandatory
        data: {disallowedIds: [1, 3, 4, 6]}
} catch(e) {
    console.warn(; // {disallowedIds: [1, 3, 4, 6]}

Inheriting from an existing Error class (the Error classes in the httpErrors module also use createError):

var httpErrors = require('httperrors');

var NotFoundUnderTheBedError = createError({
    name: 'NotFoundUnderTheBed',
    message: 'I looked under the bed, but it was not found'
}, httpErrors.NotFound);

Instances of this error walk and quack like httpErrors.NotFound instances, of course:

var ohDear = new NotFoundUnderTheBedError('No monsters today');
console.warn(ohDear.NotFound); // true
console.warn(ohDear.NotFoundUnderTheBed); // true


3-clause BSD license -- see the LICENSE file for details.