easy-app

easy-app

Easy-app is a container for applications. It allows seamless linking of different parts together in a maner similar to AMD require system. Unlike AMD it's not just about static dependencies but is also capable to link things from various runtime levels. It also facilitates composing of app from small independent pieces.

Tasks

var App = require('easy-app')
var app = App()

app.set('bar', 10)

app.def('baz', function(bar) {
  return bar * 2
})

app.def('foo', function(bar, baz) {
  return bar + baz
})

The .def method defines what is called task. Once the task and all it's dependencies were defined we can evaluate it:

app.eval('foo', function(err, foo) {
  foo.should.equal(30)
})

Task may be async

app.def('config', function(done) {
  fs.readFile('config', done)
})

So done is a special case name meaning node style callback.

You can also define dependencies explicitly:

app.def('foo', ['bar', 'baz'], function(bar, baz) {
  return bar + baz
})

Composition

For big applications definition of everything in a single global container is a bad choice. In fact we want to compose such application from small loosely coupled pieces with very few things in common. No problem:

var subapp = App() // subapp is a normal app

// define tasks as usual
// Note that we are using short names like `req`.
// Not http_request, approval_request, etc
subapp.def('req', function(bar, baz) {})

// Specify missing tasks.
subapp.importing(
  'bar',
  'baz'
)

Now we are ready to plug it in a global container:

app.install('super', subapp)

The above operation just copies everything from subapp to global container with all names been prefixed with super_. So our req task turned into

app.def('super_req', ['super_bar', 'super_baz'], function(bar, baz) {})

After (or before) installation we supposed to define missing super_bar and super_baz. If they are global shared dependencies it's better to do that via aliasing:

app
.def('bar', bar)
.def('baz', baz)

app
.install('super', subapp)
.alias('bar', 'super_bar')
.alias('baz', 'super_baz')
// or alternatively
app.install('super', subapp, {
  'bar': 'bar',
  'baz': 'baz'
})

But because .install setups aliases for undefined imports automatically we could stick with just app.install('super', subapp)

Layers

Almost always we have to deal with multiple runtime levels. For web applications they are typically "app" and "request". That's how we do that:

app.layer('app') // mark current instance to be app level
app.at('app', function() {
  app.def('config', function(done) {
    readJson('config.json', done)
  })
  app.def('db', function(config) {
    return require('monk')(config.connection_string)
  })
})
app.at('request', function() {
  app.def('session', function(db, req, done) {
    db.loadSession(req.cookie.session, done)
  })
  app.def('user', function(db, session, done) {
    db.loadUser(session.username, done)
  })
})
// ...
http.createServer(function(req, res) {
  app
  .run() // create next level instance
  .layer('request')
  .set('req', req) // seed
  .set('res', res)
  .eval('some task')
})

.at('request'), .layer('request') stuff is not really necessary for the above example.

Another way to attach task to a certain level is:

app.def('level', 'task', function(a, b) {})

Notes

Error handling

All task errors both sync and async are catched. In addition err._task property is set to the name of the task that throwed an error and err._layer is set to the name of the nearest named layer.

Control flow

All tasks are executed sequentally one after another. Dependencies are evaluated from left to right. You can rely on that.

It is convenient to specify pre-task things as an additional dependency. For example:

app.def('secretDocument', function(authorized, db) {
  return db.getSecret()
})

Evaluation of arbitrary task from within task

There is another special case dependency called eval. No surprise that it is similar to app.eval() but can be used within task and works for subapp case as expected.

app
.def('bar', bar)
.def('baz', baz)
.def('exec', function(task, eval, done) {
  eval(task, done)
})
app.run().set('task', 'bar').eval('exec') // bar executed

global
.instal('super', app)
.set('super_task', 'baz')
.eval('super_exec') // super_baz (i.e baz) executed

Doing things by convention

Sometimes you want to do things that while accomplished with regular API require a lot of repetition. For example add security check for all tasks with a certain name pattern or define subapp dependency depending on it's namespace, etc. Eventually .ontask(), .onsubapp() hooks will be provided for doing such sort of things, but now only .onsubapp() is ready.

// Hooks are just methods, not an events
// .onsubapp() is called after subapp installation but before auto-aliasing
app.onsubapp = function(ns, app) {
  // do your stuff here
  // e.g
  this.def(nsconcat(ns, 'foo'), createFoo(ns))
}

In addition there is some reflection API you might find useful:

app.importing('foo', 'bar')

app.imports('foo') //=> true
app.imports() //=> ['foo', 'bar']

app.set('foo', 'foo')
app.alias('bar', 'foo')
app.def('baz', baz)

app.defined('foo') //=> true
app.defined('bar') //=> true
app.defined('baz') //=> true
app.defined('qux') //=> false

var nsconcat = require('easy-app').nsconcat
var nssuffix = require('easy-app').nssuffix

nsconcat('hello', 'world') //=> 'hello_world'
nsconcat('', 'world') //=> 'world'

nssuffix('hello', 'hello_world') //=> 'world'
nssuffix('foo', 'hello_world') //=> null

.use()

Useful for plugins

app.use(function plugin(container, param) {
  container.should.equal(app)
  this.should.equal(app)
  param.should.equal(10)
}, 10)

Installation

via npm

npm install easy-app

via component

component install eldargab/easy-app

Related

make-flow is an util with similar ideas but intended to be just a simple control flow util rather than a full blown container.

easy-web is a new web framework under development on top of easy-app. Nearly ready but completely undocumented. Ping me if you seriously plan to use easy-app in that context and interested in some inspiration.

Special thanks

This work intially inspired by The-Kiln

License

(The MIT License)

Copyright (c) 2013 Eldar Gabdullin [e-mail]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.