Introduction

mserv-except is an error and exception handling middleware for mserv. It's simply catches exceptions that are thrown in the middleware + action pipeline and redirects them to a custom handler.

Normally when an error is thrown it gets propagated back to caller. This might not always what's wanted. mserv-except allow you to capture these errors and respond accordingly. You can even decide to rethrow the error when you are done.

Installation

$ npm i --save mserv-except

Usage

var except  = require('mserv-except'),
	service = require('mserv')()

service.use('except', except, {
	handler: function(err) {
		console.error(err.stack)
		this.res = 'error'
	}
})

Global Handlers

As of version 0.2.1, mserv-except can also register additional global handlers via an extension. By default the extension name is except but can be changed to anything else.

service.use('onError',except,{
	extension: 'onError'
	handler: function(err){
		console.log(err.stack)
		this.res = 'error'
	}
})

service.ext.onError(function*(err){
	yield /* ... insert error in a database */
	throw err
})

Error handlers are called in the reverse order they are registered but after action-level handlers. It's good measure to re-throw the error (or a modified error) unless you specifically don't want the error to bubble up to other error handlers. 

Action Specific Handlers

Actions can have their own exception handlers that get executed before any global handler. There are two ways to declare custom exception handlers. Either with a key whose value is a function or an object with a handler key whose value is a function.

service.action({
	name: 'foo',
	except: function(err) {
		// Do something specific to the action.
	},
	handler: function*() {

	}
})

service.action({
	name: 'bar',
	except: {
		handler: function(err) {
			// Do something specific to the action.
		}
	},
	handler: function*() {

	}
})