feature-toggles

Simple implementation of feature toggles for JavaScript (also called feature flipping).

Features

This module encapsulates all calls to check if a certain feature (toggle) is enabled. Furthermore it provides the possibility to have computed feature toggle values in form of functions.

Simple toggle values

Example for using plain values:

// define toggles
var toggles = {foo: true, bar: false};
 
// load them into the module
var featureToggles = require('feature-toggles');
featureToggles.load(toggles);
 
// check if a feature is enabled
if (featureToggles.isFeatureEnabled('foo')) {
    // do something
}

Computed toggle values

For computed values provide a function for the value of a feature toggle. Whenever checking if the feature is enabled the provided function will be invoked. All arguments passed to the isFeatureEnabled() call except the first one are passed on to the function.

Example:

// define a computed toggle
var toggles = {
    foo: function(a, b) {
        return (a == 'a' && b == 'b');
     }
}
 
// load them into the module
var featureToggles = require('feature-toggles');
featureToggles.load(toggles);
 
// check if a feature is enabled and provide additional arguments
if (featureToggles.isFeatureEnabled('foo', 'a', 'b') {
    // do something
}

If the function throws an exception the isFeatureEnabled() call will return false to prevent runtime crashes.

Advanced examples (pseudo code)

Enabling a toggle based on an url parameter within an express app:

var toggles = {
    foo: function(request) {
        return request.param('enableFoo');
    }
}
 
var featureToggles = require('feature-toggles');
featureToggles.load(toggles);
 
app.get('/', function(request, response) {
    if (featureToggles.isFeatureEnabled('foo', request)) {
        // do something
    }
});

Enabling a toggle based on a certain date:

var toggles = {
    foo: function() {
        var date = new Date();
        return date.getDate() > 15;
    }
}
 
var featureToggles = require('feature-toggles');
featureToggles.load(toggles);
 
if (featureToggles.isFeatureEnabled('foo')) {
    // do something
}

Express integration

Use the middleware to easily toggle features per request. This way a special version of isFeatureEnabled() is exposed to all views (res.locals). Computed toggles will automatically receive the current request and response as arguments.

var toggles = {
    foo: function(request, response) {
        return request.param('enableFoo');
    }
}

var application = express();
 
application.use(featureToggles.middleware);

- if (isFeatureEnabled('foo'))
    Foo is enabled

Alternative modules

• https://github.com/nomiddlename/flipper
• https://github.com/bigodines/feature-flipper-js