Unleash Client SDK for Node.js. It is compatible with:
$ npm install unleash-client --save
It is recommended to initialize the Unleash client SDK as early as possible in your node.js application. The SDK will set-up a in-memory repository, and poll updates from the unleash-server at regular intervals.
const { initialize } = require('unleash-client');
const unleash = initialize({
url: 'http://unleash.herokuapp.com/api/',
appName: 'my-app-name',
instanceId: 'my-unique-instance-id',
});
unleash.on('synchronized', () => {
// Unleash is ready to serve updated feature toggles.
// Check a feature flag
const isEnabled = unleash.isEnabled('some-toggle');
// Check the variant
const variant = unleash.getVariant('app.ToggleY');
});
Be aware that the initialize
function will configure a global Unleash instance. If you call this
method multiple times the global instance will be changed. If you prefer to handle the instance
yourself you should construct your own Unleash instance.
You can also use the startUnleash
function, and await
for the SDK to have fully
synchronized with the unleash-api. This allows you to secure that the SDK is not operating on
locally and potential stale feature toggle configuration.
const { startUnleash } = require('unleash-client');
const unleash = await startUnleash({
appName: 'async-unleash',
url: 'http://unleash.herokuapp.com/api/',
});
// Unleash SDK has now fresh state from the unleash-api
const isEnabled = unleash.isEnabled('Demo');
To shut down the client (turn off the polling) you can simply call the destroy-method. This is typically not required.
const { destroy } = require('unleash-client');
destroy();
The client comes with implementations for the built-in activation strategies provided by unleash.
- DefaultStrategy
- UserIdStrategy
- FlexibleRolloutStrategy
- GradualRolloutUserIdStrategy
- GradualRolloutSessionIdStrategy
- GradualRolloutRandomStrategy
- RemoteAddressStrategy
- ApplicationHostnameStrategy
Read more about the strategies in activation-strategy.md.
In order to use some of the common activation strategies you must provide a
unleash-context. This
client SDK allows you to send in the unleash context as part of the isEnabled
call:
const unleashContext = {
userId: '123',
sessionId: 'some-session-id',
remoteAddress: '127.0.0.1',
};
unleash.isEnabled('someToggle', unleashContext);
The initialize method takes the following arguments:
- url - the url to fetch toggles from. (required)
- appName - the application name / codebase name (required)
- instanceId - an unique identifier, should/could be somewhat unique
- refreshInterval - The poll-intervall to check for updates. Defaults to 15000ms.
- metricsInterval - How often the client should send metrics to Unleash API. Defaults to 60000ms.
- strategies - Custom activation strategies to be used.
- disableMetrics - disable metrics
- customHeaders - Provide a map(object) of custom headers to be sent to the unleash-server
- customHeadersFunction - Provide a function that return a Promise resolving as custom headers
to be sent to unleash-server. When options are set, this will take precedence over
customHeaders
option. - timeout - specify a timeout in milliseconds for outgoing HTTP requests. Defaults to 10000ms.
- repository - Provide a custom repository implementation to manage the underlying data
const { Strategy, initialize } = require('unleash-client');
class ActiveForUserWithEmailStrategy extends Strategy {
constructor() {
super('ActiveForUserWithEmail');
}
isEnabled(parameters, context) {
return parameters.emails.indexOf(context.email) !== -1;
}
}
initialize({
url: 'http://unleash.herokuapp.com',
strategies: [new ActiveForUserWithEmailStrategy()],
});
Its also possible to ship the unleash instance around yourself, instead of using on the default
require.cache
to have share one instance.
const { Unleash } = require('unleash-client');
const unleash = new Unleash({
appName: 'my-app-name',
url: 'http://unleash.herokuapp.com',
});
unleash.on('ready', console.log.bind(console, 'ready'));
// required error handling when using unleash directly
unleash.on('error', console.error);
The unleash instance object implements the EventEmitter class and emits the following events:
event | payload | description |
---|---|---|
ready | - | is emitted once the fs-cache is ready. if no cache file exists it will still be emitted. The client is ready to use, but might not have synchronized with the Unleash API yet. This means the SDK still can operate on stale configurations. |
synchronized | - | is emitted when the SDK has successfully synchronized with the Unleash API and has all the latest feature toggle configuration available. |
registered | - | is emitted after the app has been registered at the api server |
sent | object data |
key/value pair of delivered metrics |
count | string name, boolean enabled |
is emitted when a feature is evaluated |
warn | string msg |
is emitted on a warning |
error | Error err |
is emitted on a error |
unchanged | - | is emitted each time the client gets new toggle state from server, but nothing has changed |
changed | object data |
is emitted each time the client gets new toggle state from server and changes has been made |
Example usage:
const { initialize, isEnabled } = require('unleash-client');
const instance = initialize({
appName: 'my-app-name',
url: 'http://unleash.herokuapp.com/api/',
});
// Some useful life-cycle events
unleash.on('ready', console.log);
unleash.on('synchronized', console.log);
unleash.on('error', console.error);
unleash.on('warn', console.warn);
instance.once('registered', () => {
// Do something after the client has registered with the server api.
// NB! It might not have received updated feature toggles yet.
});
instance.once('changed', () => {
console.log(`Demo is enabled: ${isEnabled('Demo')}`);
});
unleash.on('count', (name, enabled) => console.log(`isEnabled(${name})
Sometimes you might be interested in the raw feature toggle definitions.
const {
initialize,
getFeatureToggleDefinition,
getFeatureToggleDefinitions,
} = require('unleash-client');
initialize({
url: 'http://unleash.herokuapp.com/api/',
appName: 'my-app-name',
instanceId: 'my-unique-instance-id',
});
const featureToogleX = getFeatureToggleDefinition('app.ToggleX');
const featureToggles = getFeatureToggleDefinitions();
You can manage the underlying data layer yourself if you want to. This enables you to use unleash offline, from a browser environment or implement your own caching layer. See example.
Unleash depends on a ready
event of the repository you pass in. Be sure that you emit the event
after you've initialized unleash.