Poor Man's Feature Toggle Article

_PoorMansFeatureToggle.md

This Gist and the associated files were created to support an article on Feature Flags (to be linked)

groundwork.js

function buildForecast(location) {
  return `The forecast for ${location} is "cloudy"`;
}

function appendAmountOfRain(forecast) {
  return `${forecast} with 3cm of rain`;
}

class weatherForecasterService{
  generateWeatherForecast(location) {
    const forecast = buildForecast(location);
    // We have been asked to insert appendAmountOfRain(...) here
    return forecast;
  }
}

function useWeatherForecaster(weatherForecaster) {
  console.log(weatherForecaster.generateWeatherForecast("Minnesota"))
}

const weatherForecaster = new weatherForecasterService();
useWeatherForecaster(weatherForecaster);

v1.js

const weatherForecasterService = {
  generateWeatherForecast: function (location) {
    let forecast = buildForecast(location);
    if(process.env.CURRENT_ENVIRONMENT === "nonprod") {
      forecast = appendAmountOfRain(forecast)
    }
    return forecast;
  }
}

v2.js

const features = getFeatureFlagServiceFromSomewhere()
class weatherForecasterService{
  generateWeatherForecast(location) {
    let forecast = buildForecast(location);
    if(features.isEnabled("amount-of-rain")) {
      forecast = appendAmountOfRain(forecast)
    }
    return forecast;
  }
}

v2_service.js

function environemntIsNonProduction() {
  return process.env.CURRENT_ENVIRONMENT === "nonprod";
}

const featureServiceObject = {
  isEnabled: function(flagName) {
    return environemntIsNonProduction()
  }
}

function getFeatureFlagServiceFromSomewhere() {
  return featureServiceObject;
}

v3.js

const featureDecisions = getFeatureDecisionServiceFromSomewhere()
class weatherForecasterService{
  generateWeatherForecast(location) {
    let forecast = buildForecast(location);
    if(featureDecisions.appendAmountOfRainToForecast()) {
      forecast = appendAmountOfRain(forecast)
    }
    return forecast;
  }
}

v3_featuredecision.js

const features = getFeatureFlagServiceFromSomewhere()

const featureDecisionObject = {
  appendAmountOfRainToForecast: function() {
    return features.isEnabled("amount-of-rain")
  }
}

function getFeatureDecisionServiceFromSomewhere() {
  return featureServiceObject
}

v4.js

class weatherForecasterService{  
  constructor(options) {
    this.options = options ?? {
      appendAmountOfRainToForecast: false
    }
  }
  generateWeatherForecast(location) {
    let forecast = buildForecast(location);
    if(this.options.appendAmountOfRainToForecast) {
      forecast = appendAmountOfRain(forecast)
    }
    return forecast;
  }
}

class featureAwareWeatherForecasterServiceFactory{
  build() {
    const options = {
      appendAmountOfRainToForecast: featureDecisions.appendAmountOfRainToForecast()
    }
    
    return new weatherForecasterService(options);
  }
}

const weatherForecaster = new featureAwareWeatherForecasterServiceFactory().build();