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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.

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npm install middlewarify --save


Quick Start Example

Creating a middleware:

const middlewarify = require('middlewarify');

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

const tasks = {};

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

module.exports = tasks;

...Add middleware

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

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

// add middleware to the 'create' operation

tasks.create.use(function (data) {
    console.log('middleware 1');
    data.newAttr = 2;

// Add a second middleware to the 'create' operation
tasks.create.use(function (data) {
    console.log('middleware 2. Title:', data.title);
    data.secondAttr = 3;

... Invoke all the middleware

// ... Invoking them all together
const result = tasks.create(data);

// The middleware are invoked in sequence and output:
// "middleware 1"
// "middleware 2"
// "createTask Final Fn to be invoked"

// prints: true

Middlewarify Methods

make(object, property, optMainCallback, optOptions)

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

// create a Middleware Container
const 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 from that function will be the returning value of the Middleware Container:

const val = crud.create();
// val is passed from the Main callback.

optOptions defines behavior. Both optOptions and optMainCallback are optional. 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:

  • async type: Boolean, default: false Enables asynchronous invocation of all middleware. Every middleware will be invoked asynchronously and the final returning value will be a promise.
  • 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 Before After example.
  • catchAll type Function, default: null If defined all errors will be piped to this callback, useful when Middleware is used as an Express middleware.
  • concurrent type Boolean, default: false Enables concurrent invocation of all middleware. Requires the async option to be true and cannot be used with beforeAfter option.

The use(fn) Hook.

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 available and instead you get before, after and last hooks. All hook types accept the same argument types and patterns as described bellow:

// create the Middleware Container
const 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 get 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

const req = { a: 1 };

Asynchronous Middleware Using Promises

When the option async: true is defined, all middleware get invoked asynchronously. You can return a Promise from your middleware and Middlewarify will wait for its resolution before passing control to the next one.

// create an async Middleware Container
const crud = {};
middlewarify.make(crud, 'create', fnFinal, { async: true });
crud.create.before(async () {

Invoking the Middleware

The Middleware Container is a function that accepts any number of arguments.

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

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

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

Arguments of all middleware will get:

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

    arg2 === 'bar'; // true

Middleware Results and Error Handling

When invoked, the Middleware Container will return the execution outcome. To handle any errors thrown, you simply have to wrap it in a try catch block unless you have defined a catchAll error handler. In that case the catchAll error handler will intercept any and all errors.

try {
    const retVal = crud.create(arg1, arg2, fn1);
} catch (ex) {
    // handle the error...
    console.log('Error:', ex);

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 new hooks are created on the resulting Middleware Container:

  • 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

const middlewarify = require('middlewarify');

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

After & Last Hooks get the Result as Argument

If your middleware if a Before / After type, then all .after() and .last() hooks will receive an extra argument representing the returned value of the main callback:

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 Middleware Container's Return Result

All After & Last hooks may alter the return 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"

Using Concurrent Execution

Concurrent execution will use the Promise.allSettled() function and return its raw results. So expect an array of result objects containing the status and either value on success or reason on failure.

Release History

  • v2.2.0, 14 Sep 2021
    • Introduced "concurrent" option.
  • v2.1.2, 31 May 2021
    • Updated all dependencies to latest.
  • v2.1.1, 30 Oct 2020
    • Bumped so tagged version has appropriate changelog (last release minor bump mistake).
  • v2.1.0, 30 Oct 2020
    • Updated all dependencies to latest (minor bump was a mistake, should be patch ¯_(ツ)_/¯).
  • v2.0.0, 09 Mar 2020 Breaking Changes
    • Middlewarify will now execute all middleware synchronously by default.
    • Introduced new option async to enable the asynchronous invocation.
    • Removed bluebird dependency, we are 100% native Promises.
  • v1.0.1, 30 Jan 2020
    • Updated all dependencies to latest.
  • v1.0.0, 23 Jul 2015
    • Honorary release.
    • Updated 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 Thanos Polychronakis, licensed under the ISC License.


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