Toggle Point

Feature toggles are a powerful technique, allowing teams to modify system behavior without changing code. [...] Toggles introduce complexity. We can keep that complexity in check by using smart toggle implementation practices and appropriate tools to manage our toggle configuration, but we should also aim to constrain the number of toggles in our system.

Pete Hodgson, Feature Toggles

This library takes care of the smart toggle implementation practices part by allowing you to toggle a function or object on any condition.

(right now, only function toggle is supported, with support for async functions and generators).

Written in ES6 for Node5. Support for node4 and browsers will be coming soon.

Installation

npm install --save toggle-point

Usage

import togglePoint from 'toggle-point';

function myFunctionToToggle(param) {
  return param;
}

const myToggledFunction = togglePoint(myFunctionToToggle, {
  when: (param) => param === 1,
  then: (param) => -1
});

myToggledFunction, when called, will either use the original function (when the param is anything but 1), or use the alternative version (if the param is 1)

Of course in real life, you would rather toggle depending on some context (user rights, feature activation …)

Modes

By default both the when and then are synchronous. You can use async functions too (or anything that returns a promise), by specifying mode: togglePoint.mode.async:

import togglePoint from 'toggle-point';

async function myFunctionToToggle(param) {
  return await Promise.resolve(param);
}

const myToggledFunction = togglePoint(myFunctionToToggle, {
  mode: togglePoint.mode.async,
  when: async (param) => await param === 1,
  then: async (param) => await Promise.resolve(-1)
});

The when function does not need to be async for this to work.

There is also a generator mode that allows you to toggle generator functions. Note that in generators the when function must be synchronous, as to not pollute the yield results:

import togglePoint from 'toggle-point';

function* myFunctionToToggle(param) {
  yield 1;
  yield 2;
  return param;
}

const myToggledFunction = togglePoint(myFunctionToToggle, {
  mode: togglePoint.mode.generator,
  when: (param) => param === 1,
  * then(param) {
    yield 4;
    yield 1;
    return yield param;
  }
});

The complete list of modes right now is:

(togglePoint.mode....)

• sync: Synchronous function, toggle and alternative. The default
• async: Asynchronous function, toggle and alternative. Any one of them may actually be synchronous
• generator: Generator function and alternative. Toggle must be synchronous.

Testing

The lib is 100% unit-tested using Mocha and Chai. It is developed in TDD.

Roadmap

• Toggle objects, method by method
• Toggle object properties
• Do some performance testing
• Make a version that can run on Node4 and browsers
• Deploy on npm registry (once it looks good and well documented) (still I could publish on just toggle-point, that would make it easier to use)
• Develop a companion feature management library to have a complete feature toggle system
• Use it on real production code (there's a reason why I'm developing this :) )

Building and helping

Clone the project,

npm install

In one terminal window:

npm run build:watch

In another terminal window:

npm run test:watch

All contributions and issues are welcome !