4.1.0 • Public • Published

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Rock-solid structured application layout for building APIs and web apps in Node.js.


The goal of slay is to provide the absolute minimum amount of consistency in a Node.js application without forcing an enormous amount of convention onto users. The consistency goal also centers around encouraging modularity in application-level code for maximum reuse. This is accomplished through three simple features: application layout, "preboots", and a consistent application startup.

Application layout

By convention slay looks for user-defined modules in the following locations:


This is done using standard, built-in Node.js module loading which means that each of these could be individual files of the same name instead of folders. Feel free to mix and match as your application's complexity grows. e.g.:


What is a "preboot"?

"A preboot is a middleware for application extensibility"

That is, instead of function (req, res, next) a preboot is function (app, options, done). By enforcing a consistent function signature to application extensibility all require ordering problems become trivial. For example:


module.exports = function (app, options, done) {
  // **SCHEDULE** the attachment and initialization of
  // connections to our models.


module.exports = function (app, options, next) {
  // Attach all of the models for our API / microservices
  // to the app itself and connect to them
  // (e.g. initialize TCP sockets, etc).
  app.models = require('../models');

While this may seem too obvious it does several things:

  1. Makes application extensibility simple and elegant. No complex plugin system required.
  2. Ensures that all application extensibility is ordered in a single location: lib/preboots/index.js.
  3. Encourages modularity through extending the core app by creating new preboots instead of creating an arbitrary, ad-hoc set of utility modules with a (potentially) much more complex internal dependency graph.

Consistent application startup

const slay = require('slay');
const app = new slay.App(__dirname);
app.start(options, function (err) {
  if (err) { throw err; }`Listening on ${app.config.get('http')`);

Calling app.start above will trigger two main interceptors:

  1. "setup" interceptor.
  • /preboots will be loaded in app.before('setup')
  • routers
    • app.perform('routers') triggered in app.before('setup')
    • app.router will be available by app.after('routers') or by app.perform('setup')
  1. "start" interceptor
  • lib/routes will be loaded in app.before('start')
    • lib/routes/index.js should call app.perform('actions') once to make sure all routes from app.router are loaded in the app.
  • lib/middlewares will be loaded in before('start')

For more information look at App.Bootstrap

API documentation


The App exposed by slay has all of the functionality exposed by an app created by express along with:

Method Description Inherited from
App.bootstrap Core slay bootstrap flow slay.App
app.hookable Defines a hookable action slay.App
app.stack Defines a middleware stack slay.App
app.config Config loading through nconf config preboot
app.log Logger defined through winston logger preboot
app.routes Top-level express Router routers preboot
app.preboot Schedule a preboot broadway
app.mixin Add functionality into the app broadway
app.start Start the application broadway
app.close Shutdown the application broadway
app.perform Execute a named interceptor understudy
app.before Execute before a named interceptor understudy
app.after Execute after a named interceptor understudy


Name Description Invoked by
setup Pre-start bootstrap setup slay
start Main application startup slay
routers Definition of app.routes slay
actions Critical path application functionality User


A Stack is a lightweight container for a set of before and after middlewares. This becomes very useful when you have potentially multiple routers in your application. A Stack can be defined using app.stack as follows:


module.exports = function (app, options, next) {
  // An authorization middleware for different roles
  // returns an HTTP middleware function when invoked.
  var authorize = require('./authorize');

  // Stack middlewares can be declared and used inline
      name: 'admin-only',
      before: [authorize('admin')]
    }).middleware(function (req, res, next) {
      // Dispatch (req, res) to a router.

  // Or extended from a previous declaration and used inline
      .middleware(function (req, res, next) {
        // Dispatch (req, res) to a router.

All Stack instances created by invoking app.stack will be exposed on the app.stacks object.

App startup in-detail

  1. App is bootstrapped and app.start([options], callback); is invoked.
  2. app.perform('setup') performs before "setup" interceptors (see: understudy interceptors). This executes the built-in slay preboots which:
  • Creates app.config(an instance of nconf.Provider).
  • Creates app.log (an instance of winston.Logger).
  • Creates user preboots (in your app lib/preboots[.js]?). This allows arbitrary user-defined preboots for extensibility in a sync or async fashion.
  • Schedules middlewares (in your app lib/middlewares[.js]?).
  • Schedules routes (in your app lib/routes[.js]?).
  • Schedules creation of default 404 route.
  1. Any after "setup" interceptors are invoked. (see: understudy interceptors). slay runs nothing by default here.
  2. app.perform('start') performs before "start" interceptors (see: understudy interceptors). This executes the built-in slay preboots which:
  • Schedules defaults for after "routers"
  • Invokes app.perform('routers') which performs before "routers" interceptors, adds app.routes, and performs after "routers" interceptors.
  • Invokes user-defined preboots (in your app lib/preboots[.js]?). scheduled in (2) above.
  • Invokes user-defined middlewares (in your app lib/middlewares[.js]?) scheduled in (2) above.
  • Invokes user-defined routes (in your app lib/routes[.js]?) scheduled in (2) above.
  • Adds the final 404 handler on app.routes.
  1. App.prototype._listen is invoked which creates any http and/or https servers.
  2. Any after "start" interceptors are invoked. (see: understudy interceptors). slay runs nothing by default here.
  3. The callback from app.start([options], callback); is invoked. The app is now started and ready for use.


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Contributors: Fady Matar, Charlie Robbins




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