A simple feature toggle library for Express
npm install feature-bouncer    
_A simple feature toggle library with persistance in Redis, built for Express. You can use it for feature gating, AB testing, etc._
NOTE: This is a very early development version, use at your own risk. Contributions welcome.
If you want a mature solution, these two stood out for me while researching:
- Unleash - A mature, enterprise ready, feature toggles service. Comes with a great UI and all the features you could hope for.
- React Feature Toggles - A great client-side solution, built for React.
AB testing
``ts
import * as express from 'express';
import * as Redis from 'redis';
import { FeatureBouncer, PercentageOfRequestsCheck } from 'feature-bouncer';
const app = express();
const redis = new Redis();
// Initialize FeatureBouncer
const bouncer = new FeatureBouncer({
store: redis,
features: {
example: {
// 50-50 AB testing
checks: {
'fiftyPercent': PercentageOfRequestsCheck(50),
},
// Manual override by passing in a ?abtest=show query string
overrides: {
'cheatCode': QueryStringCheck('abtest', 'show'),
}
},
}
});
// Apply middleware
app.use(bouncer.middleware);
app.get('/', async (_: any, res: any) => {
const check = await bouncer.get('example');
res.send(check ? "You passed!" : "You didn't pass :(");
});
app.listen(3000, () => console.log('listening to port 3000'));
`
`ts`
FeatureBouncer.constructor(params: {
store: any,
features: IMap
getContext?: ((request: express.Request) => IFeaturesContext) | undefined,
options?: IFeatureBouncerOptions
})
- store (object) _not implemented_ Allows persisting the data in Redis. You should be able to pass in your own client instance or configure the FeatureBouncer client.
- features (object) A Map of features you want to check. Each feature is composed of two sets of checks (regular and overrides). A feature passes when either one of the overrides checks passes, or the regular checks pass.
- getContext (function) Often times, gating features doesn't make sense without additional context (excluding the HTTP request). You can implement getContext such that you make extra data available to the checkers (user id, country, etc.) debug
- options (object) allows setting additional options, at the moment only the key is available (see debug() function).
`ts`
FeatureBouncer.middleware(
request: express.Request,
response: express.Response,
next: express.NextFunction
)
Pass to app.use() or to app.get() in order to initialize the context data, needed by the feature checkers.
Usage:
`ts`
app.use(bouncer.middleware);
// or
app.get('/yourRoute', bouncer.middleware, () => {})
`ts`
async FeatureBouncer.getX(name: string): Promise
async FeatureBouncer.get(name: string): Promise
- name (string) The name of the feature you want to check (for the AB test example above, that would be example). Returns a Promise containing the result of the check. getX() can throw, get() will just return false if there's an error.
` ts`
FeatureBouncer.debug()
If you passed { debug: true } for options in the constructor, this will return an object showing you the results for each individual checks. Checks bail early, so if it hits false before finishing all of the checks, you won't see them all in here.
This library contains a few general, but the idea is that you should build your own for anything particular to your project.
The type for the check functions is:
`
type Check = ((
idx: string,
context: IFeaturesContext
) => Promise<[string, boolean]>);
The string in the return tuple should almost always be the idx that you receive as a parameter. This is used for debugging (see debug()` method above).