Apply the middleware pattern to any property or function
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Middleware pattern implementation, robust, easy, fast. You can add two types of middleware, a single queue type using the keyword use() or a Before/After type using before() and after() hooks. All middleware accept promises or vanilla callbacks and final resolution is done using the Promises/A+ spec.

Build Status



npm install middlewarify --save


Quick Start Example

Creating a middleware:

var middlewarify = require('middlewarify');

var tasks = module.exports = {};

// this is the main callback of your middleware,
// it will be the last callback to be invoked.
function createTask() {
  console.log('createTask Final Fn to be invoked');
  return 'a value';

// Make the'create' Middleware Container.
middlewarify.make(tasks, 'create', createTask);

...Add middleware

// ... somewhere far far away in another file

var tasks = require('./tasks');

// add middleware to the 'create' operation

  console.log('middleware 1');

// add a second middleware to the 'create' operation
// this time use a promise to indicate asynchronicity
tasks.create.use(function() {
  return new Promise(function(resolve, reject) {
    console.log('middleware 2');

... Invoke all the middleware

// ... Invoking them all together
// prints
// middleware 1
// middleware 2
// createTask Final Fn to be invoked
    .then(function(val) {
        // prints: "a value"

Invoking the middleware will return a Promise, use the then function to determine all middleware including the final function invoked successfully:

tasks.create().then(function() {
  // all middleware finished.
}, function(err) {
  // Middleware failed

Using the Before / After / Last Middleware types

To use the Before/After/Last hook types all you need to do is pass the {beforeAfter: true} option to Middlewarify's make() method.

When using the beforeAfter option instead of the typical use() method three different methods are created on the resulting middleware method:

  • midd.before() Hook functions to be invoked before the main middleware function.
  • midd.after() Hook functions to be invoked after the main middleware function.
  • midd.last() Hook functions to be invoked last, after the main middleware and all middleware functions have been executed.

All added hooks are invoked in the order they were added.

Before / After / Last Middleware Example

var middlewarify = require('middlewarify');

var tasks = module.exports = {};

// This is the main callback of your middleware,
// it will be invoked after all 'before' middleware finish
// and before any 'after' middleware.
function createTask() {
    console.log('Invoked Second');
    return 999;

// Make the'create' Middleware Container using before/after hooks
middlewarify.make(tasks, 'create', createTask, {beforeAfter: true});

/** ... */

// add a before hook
tasks.create.before(function() {
    console.log('Invoked First');

// add an after hook
tasks.create.after(function() {
    console.log('Invoked Third');

// add an always LAST hook, will always invoke last
task.create.last(function() {
    console.log('Will always invoke last');

/** ... */

// invoke all middleware
    // at this point all middleware have finished.
    console.log(val); // 999
}, function(err) {
    // handle error

Middlewarify Methods

make(object, property, optMainCallback, optOptions)

The middlewarify.make() method will apply the middleware pattern to an Object's property, this property will be called the Middleware Container.

// create a Middleware Container
var crud = {};
middlewarify.make(crud, 'create');

This example has created the Middleware Container create in the object crud. crud.create() is a function that will invoke all the middleware.

You can pass a third argument, the optMainCallback, a Function. This will be the Main callback of your middleware, the result returned, or resolved if a promise is used, will get passed to the final promise:

crud.create().then(function(val) {
    // this is the final promise.
    // val is passed from the Main callback.

optOptions defines behavior. Both optOptions and optMainCallback are optional and can be interswitched, i.e. you can pass options as a third argument, read on for examples and what are the available options.

make() Options

make() accepts the following options:

  • beforeAfter type: Boolean, default: false If set to true the Before/After hooks will be used instead of the single queue use hook, which is the default, view the example displayed above.
  • catchAll type Function, default: null If defined all errors will be piped to this callback, useful when Middleware is used as Express middleware.

The use(fn) Method

The Middleware Container by default exposes a use hook so you can add any number of middleware. use() accepts any number of parameters as long they are of type Function or Array of Functions. When the Before/After flag is enabled use is no longer there and instead you get before and after hooks. All three hook types accept the same argument types and patterns as described bellow.

// create the Middleware Container
var crud = {};
middlewarify.make(crud, 'create', fnFinal);

// add 3 middleware functions
crud.create.use([fn1, fn2], fn3);

// then add another one

In the above example we added 4 middleware before the final method fnFinal will be invoked. A FIFO queue is implemented so the order of execution will be:

  1. fn1()
  2. fn2()
  3. fn3()
  4. fn4()
  5. fnFinal()

Middleware Arguments

All middleware gets invoked with the arguments that the Middleware Container was invoked with. The same number or arguments, the exact same references.

app.connect.use(function(req) {
    req.a === 1; // true
app.connect.use(function(req) {
    req.a === 2; // true


Asynchronous Middleware Using Promises

You can return a Promise from your middleware and Middlewarify will wait for its resolution before passing control to the next one.

crud.create.before(function() {
    return new Promise(function(resolve, reject) {
        // do something async...

Invoking the Middleware

The Middleware Container is nothing but a function that accepts any number of arguments.

Any argument passed to the Middleware Container will also be passed to all middleware.

var crud = {};
middlewarify.make(crud, 'create');

// run all middleware
crud.create({a: 1, b:2}, 'bar');

Arguments middleware will get:

crud.create.use(function(arg1, arg2, next) {
    arg1 === {a:1, b:2}; // true

    arg2 === 'bar'; // true


Getting the Middleware Results and Error Handling

When invoked, the Middleware Container returns a promise, with it you can check for ultimate execution outcome.

crud.create(arg1, arg2, fn1).then(function() {
    // all cool...
}, function(err) {
    // ops, handle error
    return console.error(err);

After & Last Hooks get the Result

If your middleware if a Before / After type, then all .after() hooks will receive an extra argument representing the resolving value.

middlewarify.make(crud, 'create', function(arg1, arg2) {
    return 'abc';

crud.create.after(function(arg1, arg2, val) {
    console.log(val); // prints 'abc'

crud.create(1, 2);

After & Last Hooks can alter the Result

All After & Last hooks may alter the result as long as they return any type of value except undefined.

middlewarify.make(crud, 'create', function() {
    return 'abc';

crud.create.after(function(result) {
    // return an altered outcome
    return 'def';

crud.create().then(function(result) {
    console.log(result); // prints "def"

Release History

  • v1.0.0, 23 Jul 2015
    • Honorary release.
    • Update all dependencies to latest
  • v0.4.0, 25 Jul 2014
    • Now After & Last middlewares may alter the result value by returning a non undefined value.
  • v0.3.8, 24 Jul 2014
    • Implemented .last() middleware type in beforeAfter family.
  • v0.3.7, 03 Mar 2014
    • Added catchAll option for cases where invocations have no error handlers.
  • v0.3.6, 02 Mar 2014
    • Optimizations and better handling of errors.
    • Updated to latest Bluebird, now suppresses unhandled errors.
  • v0.3.4, 19 Feb 2014
    • Update dependencies to latest.
  • v0.3.3, 15 Feb 2014
    • Resolving value now gets propagated to all .after() hooks.
  • v0.3.2, 09 Feb 2014
    • Optimize middleware invocation using Promise.try()
  • v0.3.1, 09 Feb 2014
    • Main Callback now passes value to final promise.
  • v0.3.0, 09 Feb 2014
    • Removed callback API, 100% Promise based API now.
  • v0.2.0, 08 Feb 2014
    • Major API change, introduced Promises to API.
  • v0.1.0, 28 Jan 2014
    • Added Before/After feature
    • Reorganized tests
  • v0.0.4, 10 Oct 2013
    • Added option to not throw errors
  • v0.0.3, 02 Aug 2013
    • Added a more explicit way to declare callbacks when invoking the middleware.
  • v0.0.2, 15 JuL 2013
    • Big Bang


Copyright ©2015 Thanasis Polychronakis

Licensed under the MIT License