featly

Minimalistic sync & async feature toggle.

Design goals

• Sync & async
• Minimalistic API (6 methods)
• No dependencies
• Works in the browser and in node
• Tiny [300B gzipped]

Installation

npm install featly --save

API

import featly from 'featly'

feature = featly()

feature.enable('my-feature')
feature.disable('my-feature')

feature.isEnabled('my-feature')
feature.isDisabled('my-feature')

feature.whenEnabled('my-feature', callback)
feature.whenDisabled('my-feature', callback)

That's it!

Good to know

1. Features are disabled by default.
2. You can subscribe both before and after enabling/disabling.
3. Calling enable (or disable) multiple times in a row will not cause subscribers to be called again unless the feature state actually changes.
4. Subscribers are called immediately (not deferred).
5. Subscribers are called sequentially in the order they are registered.

Examples

Use async mode for features that can be enabled at any time.

feature.whenEnabled('tracking', () => {
  $('button').on('click', () => {
    tracking.track('User clicked button')
  })
})

In the above example clicks will not be tracked if the tracking feature is never enabled.

You can enable the tracking feature with

feature.enable('tracking')

You might also want to subscribe to the tracking feature in the click handler:

$('button').on('click', () => {
  feature.whenEnabled('tracking', () => {
    tracking.track('User clicked button')
  })
})

When you enable the tracking feature, all previously registered clicks will be tracked in addition to the future ones.

Use sync mode for features which have irreversible side effects

function track(event) {
  if (feature.isEnabled('track-user-agent')) {
    event.userAgent = navigator.userAgent
  }
  event.send()
}

We query the feature state in sync mode because we only care about the state of the feature at this particular point in time.