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 CLI script. Here is how we would proceed with Knifecycle:
First, we need to handle a configuration file so we are
creating an initializer to instanciate our CONFIG service:
// bin.js
import fs from 'fs';
import Knifecycle, { initializer, constant, inject, name } from 'knifecycle';
// First of all we create a new Knifecycle instance
const $ = new Knifecycle();
// Some of our code with rely on the process environment
// let's inject it as a constant instead of directly
// pickking en vars in `process.env` to make our code
// easily testable
$.register(constant('ENV', process.env));
// Let's do so for CLI args with another constant
// in real world apps we would have create a service
// that would parse args in a complexer way
$.register(constant('ARGS', process.argv));
// We want our CLI tool to rely on some configuration
// Let's build an injectable service initializer that
// reads environment variables via an injected but
// optional `ENV` object
async function initConfig({ ENV = { CONFIG_PATH: '.' } }) {
return new Promise((resolve, reject) => {
fs.readFile(ENV.CONFIG_PATH, 'utf-8', (err, data) => {
if (err) {
reject(err);
return;
}
try {
resolve(JSON.parse(data));
} catch (err) {
reject(err);
}
});
});
}
// We are using the `initializer` decorator to
// declare our service initializer specificities
// and register it with our Knifecycle instance
$.register(
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. The `?`
// sign tells Knifecycle that the ENV dependency
// is optional
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 },
},
initConfig,
),
);
// Our CLI also uses a database so let's write an
// initializer for it:
const initDB = initializer(
{
name: 'db',
// Here we are injecting the previous `CONFIG` service
// as required so that our DB cannot be connected without
// having a proper config.
inject: ['CONFIG', 'DB_URI', '?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 },
},
async ({ CONFIG, DB_URI, log }) => {
const db = await MongoClient.connect(
DB_URI,
CONFIG.databaseOptions,
);
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,
};
},
);
// Here we are registering our initializer apart to
// be able to reuse it, we also declare the required
// DB_URI constant it needs
$.register(constant('DB_URI', 'posgresql://xxxx').register(initDB));
// Say we need to use two different DB server
// We can reuse our initializer by tweaking
// some of its properties
$.register(constant('DB_URI2', 'posgresql://yyyy'));
$.register(
// First we remap the injected dependencies. It will
// take the `DB_URI2` constant and inject it as
// `DB_URI`
inject(
['CONFIG', 'DB_URI2>DB_URI', '?log'],
// Then we override its name to make it
// available as a different service
name('db2', initDB),
),
);
// A lot of NodeJS functions have some side effects
// declaring them as constants allows you to easily
// mock/monitor/patch it. The `common-services` NPM
// module contains a few useful ones
$.register(constant('now', Date.now.bind(Date)))
.register(constant('log', console.log.bind(console)))
.register(constant('exit', process.exit.bind(process)));
// Finally, let's declare an `$autoload` service
// to allow us to load only the initializers needed
// to run the given commands
$.register(
initializer(
{
name: '$autoload',
type: 'service',
inject: ['CONFIG', 'ARGS'],
// Note that the auto loader must be a singleton
options: { singleton: true }
},
async ({ CONFIG, ARGS }) => async serviceName => {
if ('command' !== serviceName) {
throw new Error(`${serviceName} not supported!`);
}
try {
const path = CONFIG.commands + '/' + ARGS[2];
return {
path,
initializer: require(path).default,
};
} catch (err) {
throw new Error(`Cannot load ${serviceName}: ${ARGS[2]}!`);
}
},
),
);
// At this point, nothing is running. To instanciate the
// services, we have to create an execution silo using
// them. Note that we required the `$destroy` service
// implicitly created by `knifecycle`
$.run(['command', '$destroy', 'exit', 'log'])
// Here, command contains the initializer eventually
// found by automatically loading a NodeJS module
// in the above `$autoload service`. The db connections
// we only be instanciated if that command needs it
.then(async ({ command, $destroy, exit, log }) => {
try {
command();
log('It worked!');
} catch (err) {
log('It failed!', err);
} finally {
// Here we ensure every db connections are closed
// properly
await $destroy().catch(err => {
console.error('Could not exit gracefully:', err);
exit(1);
});
}
})
.catch(err => {
console.error('Could not launch the app:', err);
process.exit(1);
});
Running the following should make the magic happen:
cat "{ commands: './commands'}" > config.json
DEBUG=knifecycle CONFIG_PATH=./config.json node -r @babel/register bin.js mycommand test
// Prints: Could not launch the app: Error: Cannot load command: mycommand!
// (...stack trace)
Or at least, we still have to create commands, let's create the mycommand one:
// commands/mycommand.js
import { initializer } from './dist';
// A simple command that prints the given args
export default initializer(
{
name: 'command',
type: 'service',
// Here we could have injected whatever we declared
// in the previous file: db, now, exit...
inject: ['ARGS', 'log'],
},
async ({ ARGS, log }) => {
return () => log('Command args:', ARGS.slice(2));
},
);
So now, it works:
DEBUG=knifecycle CONFIG_PATH=./config.json node -r @babel/register bin.js mycommand test
// Prints: Command args: [ 'mycommand', 'test' ]
// It worked!
This is a very simple example but you can find a complexer CLI usage
with (metapak)[https://github.com/nfroidure/metapak/blob/master/bin/metapak.js].
Simply use the DEBUG environment variable by setting it to 'knifecycle':
DEBUG=knifecycle npm t
The output is very verbose but lead to a deep understanding of mechanisms that take place under the hood.
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. Here are the current projects that use this DI lib:
Promise.<function()>Instantiate the initializer builder service
functionApply special props to the given function from another one
functionAllows to wrap an initializer to add extra initialization steps
functionDecorator creating a new initializer with different dependencies declarations set to it.
functionDecorator creating a new initializer with some more dependencies declarations appended to it.
functionDecorator creating a new initializer with some extra informations appended to it. It is just a way for user to store some additional informations but has no interaction with the Knifecycle internals.
functionDecorator to amend an initializer options.
functionDecorator to set an initializer name.
functionDecorator to set an initializer type.
functionDecorator to set an initializer properties.
functionDecorator that creates an initializer for a constant value
functionDecorator that creates an initializer for a service
functionDecorator that creates an initializer for a provider
functionShortcut to create an initializer with a simple handler
ObjectExplode a dependency declaration an returns its parts.
Kind: global class
KnifecycleStringPromisePromisePromisePromiseCreate a new Knifecycle instance
Returns: Knifecycle - The Knifecycle instance
Example
import Knifecycle from 'knifecycle'
const $ = new Knifecycle();
KnifecycleRegister an initializer
Kind: instance method of Knifecycle
Returns: Knifecycle - The Knifecycle instance (for chaining)
| Param | Type | Description |
|---|---|---|
| initializer | function | An initializer |
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, constant, service } from 'knifecycle';
import appInitializer from './app';
const $ = new Knifecycle();
$.register(constant('ENV', process.env));
$.register(constant('OS', require('os')));
$.register(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();
$.register(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 |
| serviceName | String | Service name. |
| options | Object | Options for service retrieval |
| options.injectOnly | Boolean | Flag indicating if existing services only should be used |
| options.autoloading | Boolean | Flag to indicating $autoload dependencies on the fly loading |
| serviceProvider | String | Service provider. |
PromiseInitialize a service descriptor
Kind: instance method of Knifecycle
Returns: Promise - Service dependencies hash promise.
| Param | Type | Description |
|---|---|---|
| siloContext | Object | Current execution silo context |
| serviceName | String | Service name. |
| options | Object | Options for service retrieval |
| options.injectOnly | Boolean | Flag indicating if existing services only should be used |
| options.autoloading | Boolean | Flag to indicating $autoload dependendencies on the fly loading. |
PromiseInitialize a service dependencies
Kind: instance method of Knifecycle
Returns: Promise - Service dependencies hash promise.
| Param | Type | Description |
|---|---|---|
| siloContext | Object | Current execution silo siloContext |
| serviceName | String | Service name. |
| servicesDeclarations | String | Dependencies declarations. |
| options | Object | Options for service retrieval |
| options.injectOnly | Boolean | Flag indicating if existing services only should be used |
| options.autoloading | Boolean | Flag to indicating $autoload dependendencies on the fly loading. |
Promise.<function()>Instantiate the initializer builder service
Kind: global function
Returns: Promise.<function()> - A promise of the buildInitializer function
| Param | Type | Description |
|---|---|---|
| services | Object | The services to inject |
| services.$autoload | Object | The dependencies autoloader |
Example
import initInitializerBuilder from 'knifecycle/dist/build';
const buildInitializer = await initInitializerBuilder({
$autoload: async () => {},
});
Promise.<String>Create a JavaScript module that initialize a set of dependencies with hardcoded import/awaits.
Kind: inner method of initInitializerBuilder
Returns: Promise.<String> - The JavaScript module content
| Param | Type | Description |
|---|---|---|
| dependencies | Array.<String> | The main dependencies |
Example
import initInitializerBuilder from 'knifecycle/dist/build';
const buildInitializer = await initInitializerBuilder({
$autoload: async () => {},
});
const content = await buildInitializer(['entryPoint']);
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 initialization steps
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 different dependencies declarations set to it.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | 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 |
Example
import { inject, getInstance } from 'knifecycle'
import myServiceInitializer from './service';
getInstance()
.service('myService',
inject(['ENV'], myServiceInitializer)
);
functionDecorator creating a new initializer with some more dependencies declarations appended to it.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Description |
|---|---|---|
| dependenciesDeclarations | Array.<String> | List of dependencies declarations to append |
| initializer | function | The initializer to tweak |
Example
import { alsoInject, getInstance } from 'knifecycle'
import myServiceInitializer from './service';
getInstance()
.service('myService',
alsoInject(['ENV'], myServiceInitializer)
);
functionDecorator creating a new initializer with some extra informations appended to it. It is just a way for user to store some additional informations but has no interaction with the Knifecycle internals.
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Default | Description |
|---|---|---|---|
| extraInformations | Object | An object containing those extra informations. | |
| initializer | function | The initializer to tweak | |
| [merge] | Boolean | false | Whether the extra object should be merged with the existing one or not |
Example
import { extra, getInstance } from 'knifecycle'
import myServiceInitializer from './service';
getInstance()
.service('myService',
extra({ httpHandler: true }, 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));
functionDecorator that creates an initializer for a constant value
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Description |
|---|---|---|
| name | String | The constant's name. |
| initializer | any | The constant's value |
Example
import { Knifecycle, constant, service } from 'knifecycle';
const { printAnswer } = new Knifecycle()
.register(constant('THE_NUMBER', value))
.register(constant('log', console.log.bind(console)))
.register(service(
'printAnswer',
async ({ THE_NUMBER, log }) => () => log(THE_NUMBER),
{
inject: ['THE_NUMBER', 'log'],
}
.run(['printAnswer']);
printAnswer(); // 42
functionDecorator that creates an initializer for a service
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Description |
|---|---|---|
| name | String | The service's name. |
| initializer | function | An initializer returning the service promise |
| options | Object | Options attached to the initializer |
Example
import { Knifecycle, constant, service } from 'knifecycle';
const { printAnswer } = new Knifecycle()
.register(constant('THE_NUMBER', value))
.register(constant('log', console.log.bind(console)))
.register(service(
'printAnswer',
async ({ THE_NUMBER, log }) => () => log(THE_NUMBER),
{
inject: ['THE_NUMBER', 'log'],
}
.run(['printAnswer']);
printAnswer(); // 42
functionDecorator that creates an initializer for a provider
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Description |
|---|---|---|
| name | String | The provider's name. |
| provider | function | A provider returning the service builder promise |
| options | Object | Options attached to the initializer |
Example
import Knifecycle from 'knifecycle'
import fs from 'fs';
const $ = new Knifecycle();
$.register(provider('config', async function configProvider() {
return new Promise((resolve, reject) {
fs.readFile('config.js', function(err, data) {
let config;
if(err) {
reject(err);
return;
}
try {
config = JSON.parse(data.toString);
} catch (err) {
reject(err);
return;
}
resolve({
service: config,
});
});
});
}));
functionShortcut to create an initializer with a simple handler
Kind: global function
Returns: function - Returns a new initializer
| Param | Type | Default | Description |
|---|---|---|---|
| handlerFunction | function | The handler function | |
| [dependencies] | Array | [] | The dependencies to inject in it |
| [extra] | Object | Optional extra data to associate with the handler |
Example
import { initializer, getInstance } from 'knifecycle';
getInstance()
.register(handler(getUser, ['db', '?log']));
const QUERY = `SELECT * FROM users WHERE id=$1`
async function getUser({ db }, userId) {
const [row] = await db.query(QUERY, userId);
return row;
}
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 483 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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