knifecycle
Advanced tools
Manage your NodeJS processes's lifecycle.
Most (maybe all) applications rely on two kinds of dependencies.
The code dependencies are fully covered by require/system
modules in a testable manner (with mockery or System
directly). There is no need for another dependency management
system if those libraries are pure functions (involve no
global states at all).
Unfortunately, applications often rely on global states
where the JavaScript module system shows its limits. This
is where knifecycle enters the game.
It is largely inspired by the Angular service system except it should not provide code but access to global states (time, filesystem, db). It also have an important additional feature to shutdown processes which is really useful for back-end servers and doesn't exists in Angular.
You may want to look at the
architecture notes to better handle the
reasonning behind knifecycle and its implementation.
At this point you may think that a DI system is useless. My advice is that it depends. But at least, you should not make a definitive choice and allow both approaches. See this Stack Overflow anser for more context about this statement.
knifecycle impeach that while providing an
$injector service à la Angular to allow accessing existing
services references if you really need to;Using knifecycle is all about declaring the services our
application needs and running your application over it.
Let's say we are building a web service. First, we need to
handle a configuration file so we are creating an
initializer to instanciate our CONFIG service:
// services/config.js
import fs from 'fs';
import { initializer } from 'knifecycle';
// We are using the `initializer` decorator to
// declare our service initializer specificities
// Note that the initializer` decorator is pure
// so it just adds static informations and do not
// register the initializer to the provider yet.
export const initConfig = initializer({
// we have to give our final service a name
// for further use in other services injections
name: 'CONFIG',
// we will need an `ENV` variable in the initializer
// so adding it in the injected dependencies.
inject: ['ENV'],
// our initializer is simple so we use the `service`
// type for the initializer which just indicate that
// the initializer will return a promise of the actual
// service
type: 'service',
// We don't want to read the config file everytime we
// inject it so declaring it as a singleton
options: { singleton: true },
// Here is the actual initializer implementation, you
// can notice that it expect the `ENV` dependency to
// be set as a property of an object in first argument.
}, ({ ENV }) => {
return new Promise((resolve, reject) {
fs.readFile(ENV.CONFIG_PATH, function(err, data) {
if(err) {
return reject(err);
}
try {
resolve(JSON.parse(data));
} catch (err) {
reject(err);
}
}, 'utf-8');
});
Our service also uses a database so let's write an initializer for it:
// services/db.js
import { initializer } from 'knifecycle';
const initDB = initializer({
name: 'db',
// Here we are injecting the previous `CONFIG` service
// plus an optional one. If it does not exist then it
// will silently fail and the service will be undefined.
inject: ['CONFIG', '?log'],
// The initializer type is slightly different. Indeed,
// we need to manage the database connection errors
// and wait for it to flush before shutting down the
// process.
// A service provider returns a promise of a provider
// descriptor exposing:
// - a mandatory `service` property containing the
// actual service;
// - an optional `dispose` function allowing to
// gracefully close the service;
// - an optional `fatalErrorPromise` property to
// handle the service unrecoverable failure.
type: 'provider',,
options: { singleton: true },
}, ({ CONFIG, log }) {
return MongoClient.connect(CONFIG.DB_URI)
.then(function(db) {
let fatalErrorPromise = new Promise((resolve, reject) {
db.once('error', reject);
});
// Logging only if the `log` service is defined
log && log('info', 'db service initialized!');
return {
service: db,
dispose: db.close.bind(db, true),
fatalErrorPromise,
};
});
}
We need a last initializer for the HTTP server itself:
// services/server.js
import { initializer } from 'knifecycle';
import express from 'express';
const initDB = initializer({
name: 'server',
inject: ['ENV', 'CONFIG', '?log'],
options: { singleton: true },
}, ({ ENV, CONFIG, log }) => {
const app = express();
return new Promise((resolve, reject) => {
const port = ENV.PORT || CONFIG.PORT;
const server = app.listen(port, () => {
log && log('info', `server listening on port ${port}!`);
resolve(server);
});
}).then(function(server) {
let fatalErrorPromise = new Promise((resolve, reject) {
app.once('error', reject);
server.once('error', reject);
});
function dispose() {
return new Promise((resolve, reject) => {
server.close((err) => {
if(err) {
reject(err);
return;
}
resolve();
})
});
}
return {
service: app,
dispose,
fatalErrorPromise,
};
});
});
Great! We are ready to make it work altogether:
import { getInstance } from 'knifecycle';
import initConfig from 'services/config';
import initDB from 'services/db';
import initServer from 'services/server';
// We need only one Knifecycle instance so using
// a the singleton API
getInstance()
// Registering our initializers
.register(initConfig)
.register(initServer)
.register(initDB)
// Let's say we need to have another `db`
// service pointing to another db server.
.register(
// First we remap the injected dependencies. It will
// take the `DB2_CONFIG` service and inject it as
// `CONFIG`
inject(['DB2_CONFIG>CONFIG', '?log'],
// Then we override its name
name('db2', initDB)
)
)
// Finally, we have to create the `DB2_CONFIG` service
// on which the `db2` service now depends on
.register(name('DB2_CONFIG', inject(['CONFIG'], ({ CONFIG }) => {
// Let's just pick up the `db2` uri in the `CONFIG`
// service
return Promise.resolve({
DB_URI: CONFIG.DB2_URI,
});
})))
// Add the process environment as a simple constant
.constant('ENV', process.env)
// Add a function providing the current timestamp
.constant('now', Date.now.bind(Date))
// Add a delay function
.constant('delay', Promise.delay.bind(Promise))
// Add process lifetime utils
.constant('waitSignal', function waitSignal(signal) {
return new Promise((resolve, reject) => {
process.once(signal, resolve.bind(null, signal));
});
})
.constant('exit', process.exit.bind(exit))
// Setting a route to serve the current timestamp.
.register(name('timeRoute',
inject(
['server', 'now', '?log'],
({ server: app, now, log }) {
return Promise.resolve()
.then(() => {
app.get('/time', (req, res, next) => {
const curTime = now();
log && log('info', 'Sending the current time:', curTime);
res.status(200).send(curTime);
});
});
}
)
))
// At this point, nothing is running. To instanciate
// services, we have to create an execution silo using
// them. Note that we required the `$destroy` service
// implicitly created by `knifecycle`
.run(['server', 'timeRoute', 'waitSignal', 'exit', '$destroy'])
// Note that despite we injected them, we do not take
// back the `server` and `timeRoute` services. We only
// need them to get up and running but do not need to
// operate on them
.then(({ waitSignal, exit, $destroy }) {
// We want to exit gracefully when a SIG_TERM/INT
// signal is received
Promise.any([
waitSignal('SIGINT'),
waitSignal('SIGTERM'),
])
// The `$destroy` service will disable all silos
// progressively and then the services they rely
// on to finally resolve the returned promise
// once done
.then($destroy)
.then(() => {
// graceful shutdown was successful let's exit
// in peace
exit(0);
})
.catch((err) => {
console.error('Could not exit gracefully:', err);
exit(1);
});
})
.catch((err) => {
console.error('Could not launch the app:', err);
process.exit(1);
});
Simply use the DEBUG environment variable by setting it to 'knifecycle':
DEBUG=knifecycle npm t
The scope of this library won't change. However the plan is:
I'll also share most of my own initializers and their stubs/mocks in order to let you reuse it through your projects easily.
functionApply special props to the given function from another one
functionAllows to wrap an initializer to add extra
functionDecorator creating a new initializer with some dependencies declarations appended to it.
functionDecorator to amend an initializer options.
functionDecorator to set an initializer name.
functionDecorator to set an initializer type.
functionDecorator to set an initializer properties.
ObjectExplode a dependency declaration an returns its parts.
Kind: global class
KnifecycleKnifecycleKnifecycleStringPromisePromisePromisePromiseCreate a new Knifecycle instance
Returns: Knifecycle - The Knifecycle instance
Example
import Knifecycle from 'knifecycle'
const $ = new Knifecycle();
KnifecycleRegister a constant service
Kind: instance method of Knifecycle
Returns: Knifecycle - The Knifecycle instance (for chaining)
| Param | Type | Description |
|---|---|---|
| constantName | String | The name of the service |
| constantValue | any | The constant value |
Example
import Knifecycle from 'knifecycle'
const $ = new Knifecycle();
// Expose the process env
$.constant('ENV', process.env);
// Expose a time() function
$.constant('time', Date.now.bind(Date));
KnifecycleRegister a service initializer
Kind: instance method of Knifecycle
Returns: Knifecycle - The Knifecycle instance (for chaining)
| Param | Type | Description |
|---|---|---|
| serviceName | String | Service name |
| initializer | function | An initializer returning the service promise |
| options | Object | Options attached to the initializer |
Example
import Knifecycle from 'knifecycle'
import fs from 'fs';
const $ = new Knifecycle();
$.service('config', configServiceInitializer, {
singleton: true,
});
function configServiceInitializer({ CONFIG_PATH }) {
return new Promise((resolve, reject) {
fs.readFile(CONFIG_PATH, function(err, data) {
if(err) {
return reject(err);
}
try {
resolve(JSON.parse(data));
} catch (err) {
reject(err);
}
}, 'utf-8');
}
KnifecycleRegister a provider initializer
Kind: instance method of Knifecycle
Returns: Knifecycle - The Knifecycle instance (for chaining)
| Param | Type | Description |
|---|---|---|
| serviceName | String | Service name resolved by the provider |
| initializer | function | An initializer returning the service promise |
| options | Object | Options attached to the initializer |
Example
import Knifecycle from 'knifecycle'
import fs from 'fs';
const $ = new Knifecycle();
$.provider('config', function configProvider() {
return new Promise((resolve, reject) {
fs.readFile('config.js', function(err, data) {
let config;
if(err) {
return reject(err);
}
try {
config = JSON.parse(data.toString);
} catch (err) {
return reject(err);
}
resolve({
service: config,
});
});
});
});
StringOutputs a Mermaid compatible dependency graph of the declared services. See Mermaid docs
Kind: instance method of Knifecycle
Returns: String - Returns a string containing the Mermaid dependency graph
| Param | Type | Description |
|---|---|---|
| options | Object | Options for generating the graph (destructured) |
| options.shapes | Array.<Object> | Various shapes to apply |
| options.styles | Array.<Object> | Various styles to apply |
| options.classes | Object | A hash of various classes contents |
Example
import { Knifecycle, inject } from 'knifecycle';
import appInitializer from './app';
const $ = new Knifecycle();
$.constant('ENV', process.env);
$.constant('OS', require('os'));
$.service('app', inject(['ENV', 'OS'], appInitializer));
$.toMermaidGraph();
// returns
graph TD
app-->ENV
app-->OS
PromiseCreates a new execution silo
Kind: instance method of Knifecycle
Returns: Promise - Service descriptor promise
| Param | Type | Description |
|---|---|---|
| dependenciesDeclarations | Array.<String> | Service name. |
Example
import Knifecycle from 'knifecycle'
const $ = new Knifecycle();
$.constant('ENV', process.env);
$.run(['ENV'])
.then(({ ENV }) => {
// Here goes your code
})
PromiseInitialize or return a service descriptor
Kind: instance method of Knifecycle
Returns: Promise - Service dependencies hash promise.
| Param | Type | Description |
|---|---|---|
| siloContext | Object | Current execution silo context |
| injectOnly | Boolean | Flag indicating if existing services only should be used |
| serviceName | String | Service name. |
| serviceProvider | String | Service provider. |
PromiseInitialize a service
Kind: instance method of Knifecycle
Returns: Promise - Service dependencies hash promise.
| Param | Type | Description |
|---|---|---|
| siloContext | Object | Current execution silo context |
| serviceName | String | Service name. |
| serviceProvider | String | Service provider. |
PromiseInitialize a service dependencies
Kind: instance method of Knifecycle
Returns: Promise - Service dependencies hash promise.
| Param | Type | Default | Description |
|---|---|---|---|
| siloContext | Object | Current execution silo siloContext | |
| serviceName | String | Service name. | |
| servicesDeclarations | String | Dependencies declarations. | |
| injectOnly | Boolean | false | Flag indicating if existing services only should be used |
KnifecycleReturns a Knifecycle instance (always the same)
Kind: static method of Knifecycle
Returns: Knifecycle - The created/saved instance
Example
import { getInstance } from 'knifecycle'
const $ = getInstance();
functionApply special props to the given function from another one
Kind: global function
Returns: function - The newly built function
| Param | Type | Default | Description |
|---|---|---|---|
| from | function | The initialization function in which to pick the props | |
| to | function | The initialization function from which to build the new one | |
| [amend] | Object | {} | Some properties to override |
functionAllows to wrap an initializer to add extra
Kind: global function
Returns: function - The new initializer
| Param | Type | Description |
|---|---|---|
| wrapper | function | A function taking dependencies and the base service in arguments |
| baseInitializer | function | The initializer to decorate |
functionDecorator creating a new initializer with some dependencies declarations appended to it.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Default | Description |
|---|---|---|---|
| dependenciesDeclarations | Array.<String> | List of dependencies declarations to declare which services the initializer needs to resolve its own service. | |
| initializer | function | The initializer to tweak | |
| [merge] | Boolean | false | Whether dependencies should be merged with existing ones or not |
Example
import { inject, getInstance } from 'knifecycle'
import myServiceInitializer from './service';
getInstance()
.service('myService',
inject(['ENV'], myServiceInitializer)
);
functionDecorator to amend an initializer options.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Default | Description |
|---|---|---|---|
| options | Object | Options to set to the initializer | |
| options.singleton | Object | Define the initializer service as a singleton (one instance for several runs) | |
| initializer | function | The initializer to tweak | |
| [merge] | function | true | Whether options should be merged or not |
Example
import { inject, options, getInstance } from 'knifecycle';
import myServiceInitializer from './service';
getInstance()
.service('myService',
inject(['ENV'],
options({ singleton: true}, myServiceInitializer)
)
);
functionDecorator to set an initializer name.
Kind: global function
Returns: function - Returns a new initializer with that name set
| Param | Type | Description |
|---|---|---|
| name | String | The name of the service the initializer resolves to. |
| initializer | function | The initializer to tweak |
Example
import { name, getInstance } from 'knifecycle';
import myServiceInitializer from './service';
getInstance()
.register(name('myService', myServiceInitializer));
functionDecorator to set an initializer type.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Description |
|---|---|---|
| type | String | The type to set to the initializer. |
| initializer | function | The initializer to tweak |
Example
import { name, type, getInstance } from 'knifecycle';
import myServiceInitializer from './service';
getInstance()
.register(
type('service',
name('myService',
myServiceInitializer
)
)
);
functionDecorator to set an initializer properties.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Description |
|---|---|---|
| properties | Object | Properties to set to the service. |
| initializer | function | The initializer to tweak |
Example
import { initializer, getInstance } from 'knifecycle';
import myServiceInitializer from './service';
getInstance()
.register(initializer({
name: 'myService',
type: 'service',
inject: ['ENV'],
options: { singleton: true }
}, myServiceInitializer));
ObjectExplode a dependency declaration an returns its parts.
Kind: global function
Returns: Object - The various parts of it
| Param | Type | Description |
|---|---|---|
| dependencyDeclaration | String | A dependency declaration string |
Example
parseDependencyDeclaration('pgsql>db');
// Returns
{
serviceName: 'pgsql',
mappedName: 'db',
optional: false,
}
FAQs
Manage your NodeJS processes's lifecycle automatically with an unobtrusive dependency injection implementation.
The npm package knifecycle receives a total of 876 weekly downloads. As such, knifecycle popularity was classified as not popular.
We found that knifecycle demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 0 open source maintainers collaborating on the project.
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