ember-launch-darkly

ember-launch-darkly

This addon wraps the Launch Darkly feature flagging service and provides helpers to implement feature flagging in your application

Installation

$ ember install ember-launch-darkly

Configuration

ember-launch-darkly can be configured from config/environment.js as follows:

module.exports = function(environment) {
  let ENV = {
    launchDarkly: {
      // options
    }
  };

  return ENV
};

ember-launch-darkly supports the following configuration options:

clientSideId (required)

The client side ID generated by Launch Darkly which is available in your account settings page. See the Launch Darkly docs for more information on how the client side ID is used.

local

Specify that you'd like to pull feature flags from your local config instead of remotely from Launch Darkly. This is likely appropriate when running in the development environment or an external environment for which you don't have Launch Darkly set up.

This option will also make the launch darkly service available in the browser console so that feature flags can be enabled/disabled manually.

Default: false in production, true in all other environments

localFeatureFlags

A list of initial values for your feature flags. This property is only used when local: true to populate the list of feature flags for environments such as local development where it's not desired to store the flags in Launch Darkly.

Default: null

streaming

Streaming options for the feature flags for which you'd like to subscribe to realtime updates. See the Streaming Feature Flags section for more detailed info on what the possible options are for streaming flags.

Default: false

Content Security Policy

If you have CSP enabled in your ember application, you will need to add Launch Darkly to the connect-src like so:

// config/environment.js

module.exports = function(environment) {
  let ENV = {
    //snip

    contentSecurityPolicy: {
      'connect-src': ['https://*.launchdarkly.com']
    }

    //snip
  };
};

Usage

Launch Darkly Service

ember-launch-darkly automatically injects the launch darkly service, as launchDarkly in to the following Ember objects:

• all routes
• all controllers
• all components
• router:main

This means that it can be accessed without an explicit injection, like so:

// /app/application/route.js

import Route from '@ember/routing/route';

export default Route.extend({
  model() {
    let user = {
      key: 'aa0ceb',
      anonymous: true
    };

    return this.launchDarkly.initialize(user);
  }
});

Due to Ember not allowing auto injection of a service in to another service, we are currently unable to auto inject launchDarkly in to other services. This means that if you would like to check for Launch Darkly flags in your service, you will need to explicitly inject the launchDarkly service yourself.

Initialize

Before being used, Launch Darkly must be initialized. This should happen early so choose an appropriate place to make the call such as an application initializer or the application route.

The initialize() function returns a promise that resolves when the Launch Darkly client is ready so Ember will wait until this happens before proceeding.

The user key is the only required attribute, see the Launch Darkly documentation for the other attributes you can provide.

// /app/application/route.js

import Route from '@ember/routing/route';

export default Route.extend({
  model() {
    let user = {
      key: 'aa0ceb',
      anonymous: true
    };

    return this.launchDarkly.initialize(user);
  }
});

Identify

If you initialized Launch Darkly with an anonymous user and want to re-initialize it for a specific user to receive the flags for that user, you can use identify. This can only be called after initialize has been called.

// /app/session/route.js

import Route from '@ember/routing/route';

export default Route.extend({
  session: service(),

  model() {
    return this.session.getSession();
  },

  afterModel(session) {
    let user = {
      key: session.get('user.id'),
      firstName: session.get('user.firstName'),
      email: session.get('user.email')
    };

    return this.launchDarkly.identify(user);
  }
});

Templates

ember-launch-darkly provides a variation helper to check your feature flags in your handlebars templates.

If your feature flag is a boolean based flag, you might use it in an {{if}} like so:

{{#if (variation "new-login-screen")}}
  {{login-screen}}
{{else}}
  {{old-login-screen}}
{{/if}}

If your feature flag is a multivariate based flag, you might use it in an {{with}} like so:

{{#with (variation "new-login-screen") as |variant|}}
  {{#if (eq variant "login-screen-a")}
    {{login-screen-a}}
  {{else if (eq variant "login-screen-b")}}
    {{login-screen-b}}
  {{/if}}
{{else}}
  {{login-screen}}
{{/with}}

Javascript

If your feature flag is a boolean based flag, you might use it in a function like so:

// /app/components/login-page/component.js

import Component from '@ember/component';
import { computed } from '@ember/object';

export default Component.extend({
  actions: {
    getPrice() {
      if (this.launchDarkly.variation('new-price-plan')) {
        return 99.00;
      }

      return 199.00;
    },
  }
});

If your feature flag is a multivariate based flag, you might use it in a function like so:

// /app/components/login-page/component.js

import Component from '@ember/component';
import { computed } from '@ember/object';

export default Component.extend({
  actions: {
    getPrice() {
      switch (this.launchDarkly.variation('new-pricing-plan')) {
        case 'plan-a':
          return 99.00;
        case 'plan-b':
          return 89.00
        case 'plan-c':
          return 79.00
      }

      return 199.00;
    }
  }
});

And if you want to check a flag in a computed property, and have it recompute when the flag changes, you'll want to make sure you add the flag as a dependent key to the CP, as follows:

// /app/components/login-page/component.js

import Component from '@ember/component';
import { computed } from '@ember/object';

export default Component.extend({
  price: computed('launchDarkly.new-price-plan', function() {
    if (this.launchDarkly['new-price-plan']) {
      return 99.00;
    }

    return 199.00;
  })
});

[EXPERIMENTAL] variation Javascript helper

ember-launch-darkly provides a special, experimental, variation import that can be used in Javascript files such as Components, to make the invocation and checking of feature flags a little nicer in the JS code.

This helper is backed by a Babel transform that essentially replaces the helper with the code above in the Javascript section. The main benefits this helper provides is:

• Automatically adds feature flags as dependent keys to computed properties so they are recalculated when flags change
• Removes boiler plate launch darkly code (injection of service, referencing service in functions, etc)
• Provide a syntax that is parallel to the variation helper used in templates

The babel transform that replaces this variation helper in the JS code is experimental. YMMV.

If you would like to try it out, simply enable it in your ember-cli-build.js as follows:

// ember-cli-build.js

const EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function(defaults) {
  let app = new EmberApp(defaults, {
    babel: {
      plugins: [ require.resolve('ember-launch-darkly/babel-plugin') ]
    }
  });

  return app.toTree();
};

Then import the helper from ember-launch-darkly and use it as follows:

// /app/components/login-page/component.js

import Component from '@ember/component';

import { variation } from 'ember-launch-darkly';

export default Component.extend({
  price() {
    if (variation('new-pricing-plan')) {
      return 99.00;
    }

    return 199.00;
  }
});

If you would like the feature flag to recompute a computed property when it changes, you will need to also use the computedWithVariation import, like so:

// /app/components/login-page/component.js

import Component from '@ember/component';
import { variation, computedWithVariation as computed } from 'ember-launch-darkly';

export default Component.extend({
  price: computed(function() {
    if (variation('new-pricing-plan')) {
      return 99.00;
    }

    return 199.00;
  })
});

The computedWithvariation import is literally a direct re-export of the @ember/object computed. We need to re-export it so that we can signal to the babel transform where to auto insert the feature flag dependent keys. Because computedWithVariation is a re-export you can alias it as computed (like above) and use it anywhere you would use a normal computed.

For reference, the babel transform should transform the above code in to, roughly, the following:

// /app/components/login-page/component.js

import Component from '@ember/component';
import { computed } from '@ember/object';

export default Component.extend({
  price: computed('launchDarkly.new-pricing-plan', function() {
    if (this.launchDarkly['new-pricing-plan']) {
      return 99.00;
    }

    return 199.00;
  })
});

It's important to note that the variation helper will only work when used inside objects that have an owner. This is because the helper is transformed in to a call to this.launchDarkly which is an injected service. Therefore, the variation helper will not work in a computed returned from, say, a function. Like so:

export default function myCoolFn() {
  if (variation('foo')) {
    return 'I love cheese';
  }

  return 'I love bacon';
}

For the reason above, if you would like to use the variation helper in one of your own objects that extends EmberObject, you will need to create the EmberObject instance with an owner injection, like so:

// /app/components/login-page/component.js

import Component from '@ember/component';
import EmberObject from '@ember/object';
import { getOwner } from '@ember/application';

const MyFoo = EmberObject.extend({
  price() {
    return variation('my-price');
  }
});

export default Component.extend({
  createFoo() {
    let owner = getOwner(this);

    return MyFoo.create(owner.ownerInjection(), {
      someProp: 'bar'
    });
  }
});

As this babel transform is experimental, it does not currently support the following:

• Native classes
• Decorators

We will endeavour to add support for these things in the future.

Local feature flags

When local: true is set in the Launch Darkly configuration, ember-launch-darkly will retrieve the feature flags and their values from config/environment.js instead of the Launch Darkly service. This is useful for development purposes so you don't need to set up a new environment in Launch Darkly, your app doesn't need to make a request for the flags, and you can easily change the value of the flags from the browser console.

The local feature flags are defined in config/environment.js like so:

let ENV = {
  launchDarkly: {
    local: true,
    localFeatureFlags: {
      'apply-discount': true,
      'new-pricing-plan': 'plan-a'
    }
  }
}

When local: true, the Launch Darkly feature service is available in the browser console via window.ld. The service provides the following helper methods to manipulate feature flags:

> ld.variation('new-pricing-plan', 'plan-a') // return the current value of the feature flag providing a default if it doesn't exist

> ld.setVariation('new-pricing-plan', 'plan-x') // set the variation value

> ld.enable('apply-discount') // helper to set the return value to `true`
> ld.disable('apply-discount') // helper to set the return value to `false`

> ld.allFlags() // return the current list of feature flags and their values

> ld.user() // return the user that the client has been initialized with

Streaming Feature Flags

Launch Darkly supports the ability to subscribe to changes to feature flags so that apps can react in real-time to these changes. The streaming configuration option allows you to specify, in a couple of ways, which flags you'd like to stream.

To disable streaming completely, use the following configuration:

launchDarkly: {
  streaming: false
}

Note, this is the default behaviour if the streaming option is not specified.

To stream all flags, use the following configuration:

launchDarkly: {
  streaming: true
}

To get more specific, you can select to stream all flags except those specified:

launchDarkly: {
  streaming: {
    allExcept: ['apply-discount', 'new-login']
  }
}

And, finally, you can specify only which flags you would like to stream:

launchDarkly: {
  streaming: {
    'apply-discount': true
  }
}

As Launch Darkly's realtime updates to flags uses the Event Source API, certain browsers will require a polyfill to be included. ember-launch-darkly uses EmberCLI targets to automatically decide whether or not to include the polyfill. Ensure your project contains a valid config/targets.js file if you require this functionality.

Test Helpers

Acceptance Tests

Add the setupLaunchDarkly hook to the top of your test file. This will ensure that Launch Darkly uses a test stub client which defaults your feature flags to false instead of using what is defined in the localFeatureFlags config. This allows your tests to start off in a known default state.

import { module, test } from 'qunit';
import { visit, currentURL, click } from '@ember/test-helpers';
import { setupApplicationTest } from 'ember-qunit';

import { setupLaunchDarkly } from 'ember-launch-darkly/test-support';

module('Acceptance | Homepage', function(hooks) {
  setupApplicationTest(hooks);
  setupLaunchDarkly(hooks);

  test('links go to the new homepage', async function(assert) {
    await visit('/');
    await click('a.pricing');

    assert.equal(currentRoute(), 'pricing', 'Should be on the old pricing page');
  });
});

ember-launch-darkly provides a test helper, withVariation, to make it easy to turn feature flags on and off in acceptance tests.

module('Acceptance | Homepage', function(hooks) {
  setupApplicationTest(hooks);
  setupLaunchDarkly(hooks);

  test('links go to the new homepage', async function(assert) {
    this.withVariation('new-pricing-plan', 'plan-a');

    await visit('/');
    await click('a.pricing');

    assert.equal(currentRoute(), 'pricing', 'Should be on the old pricing page');
  });
});

Integration Tests

Use the setupLaunchDarkly hook and withVariation helper in component tests to control feature flags as well.

import { module, test } from 'qunit';
import { setupRenderingTest } from 'ember-qunit';
import { render } from '@ember/test-helpers';
import hbs from 'htmlbars-inline-precompile';

import { setupLaunchDarkly } from 'ember-launch-darkly/test-support';

module('Integration | Component | foo', function(hooks) {
  setupRenderingTest(hooks);
  setupLaunchDarkly(hooks);

  test('new pricing', async function(assert) {
    await render(hbs`
      {{#if (variation "new-pricing-page")}}
        <h1 class="price">£ 99</h1>
      {{else}}
        <h1 class="price">£ 199</h1>
      {{/if}}
    `);

    this.withVariation('new-pricing-page');

    assert.equal(this.element.querySelector('.price').textContent.trim(), '£ 99', 'New pricing displayed');
  });
});

TODO

• Implement support for secure mode (#9)

_{Made with :heart: by The Ember Launch Darkly Team}