| module.exports = CustomError; | |
| function CustomError(message, extra) { | |
| Error.call(this); | |
| Error.captureStackTrace(this, this.constructor); | |
| this.name = this.constructor.name; | |
| this.message = message; | |
| this.extra = extra; | |
| } | |
| require('util').inherits(CustomError, Error); |
It's nice to be able to distinguish error types by classes. But it's a bit tricky to correctly create a custom error class in Node.js, so here is an example.
This example also shows how to add an extra parameter called extra that will be stored as a property on the error.
Example usage:
var CustomError = require('./errors/custom-error');
function doSomethingBad() {
throw new CustomError('It went bad!', 42);
}| // Mini test suite for our custom error | |
| var assert = require('assert'); | |
| var CustomError = require('./errors/custom-error'); | |
| function doSomethingBad() { | |
| throw new CustomError('It went bad!', 42); | |
| } | |
| try { | |
| doSomethingBad(); | |
| } catch (err) { | |
| // The name property should be set to the error's name | |
| assert(err.name = 'CustomError'); | |
| // The error should be an instance of its class | |
| assert(err instanceof CustomError); | |
| // The error should be an instance of builtin Error | |
| assert(err instanceof Error); | |
| // The error should be recognized by Node.js' util#isError | |
| assert(require('util').isError(err)); | |
| // The error should have recorded a stack | |
| assert(err.stack); | |
| // toString should return the default error message formatting | |
| assert.strictEqual(err.toString(), | |
| 'CustomError: It went bad!'); | |
| // The stack should start with the default error message formatting | |
| assert.strictEqual(err.stack.split('\n')[0], | |
| 'CustomError: It went bad!'); | |
| // The first stack frame should be the function where the error was thrown. | |
| assert.strictEqual(err.stack.split('\n')[1].indexOf('doSomethingBad'), 7); | |
| // The extra property should have been set | |
| assert.strictEqual(err.extra, 42); | |
| } | |
| // Spoiler: It passes! |