Checking feature flags in client-side application

[ropez]

I'm trying to figure out how to use Feature flags in a front-end application (SPA). Specifically, an application build with Vue,js, but it would have been the same if the application was build for instance with React or Angular.

I find it difficult to understand how the @azure/app-configuration package is helpful for this scenario.

• The package seems to have a lot of functionality that is not needed. I'm not interested in setting or editing any configuration values.
• All the examples in the documentation seems to be focused on editing values. So for me, is seems like the package is meant for managing the application, not to be used in the application itself.
• The package adds something like 120 KB to the application bundle, twice as much as Vue.js itself
• The one thing I need to do, which is to check if a feature flag is enabled or not, is not shown in any of the examples. I found some examples in other places, but they include manually parsing JSON, and don't seem to take targeting percentages into account.

So my question is, how to I actually use a feature flag in my application. I'm looking for something like this:

if (featureFlag.isEnabled()) {
  showFeature();
}

I would also expect a feature flag management system to be able to track changes and update the application (e.g. using polling or websockets subscription etc).

Is there at all a javascript client that supports these use cases, or is it something that users are expected to implement themselves?

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Document Details

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• ID: 7e2d3a86-f4a2-2c5d-6bc5-e5bea7dcb375
• Version Independent ID: bf71f0f5-fec7-6fc3-e1b2-80c80a6bdc0e
• Content: Use App Configuration client library for JavaScript
• Content Source: docs-ref-services/latest/app-configuration-readme.md
• Service: azure
• GitHub Login: @maggiepint
• Microsoft Alias: magpint

[HarshaNalluru]

Hey @ropez,

Thanks for reaching out.
Feature flag support in the SDK is currently under development.
#14342 PR adds the support you expect w.r.t feature flags.

We'll be releasing a new preview version 1.2.0-beta.1 version for @azure/app-configuration this week with the feature flag support as part of the new features.

The current estimate is that the new 1.2.0 version will be released for GA(General Availability) in the June-July timeframe.

[ropez]

Thanks for the reply, @HarshaNalluru

Unfortunately, looking through the PR that you've linked to, the functionality seems to be consistent with the points I made above. All the examples and test cases seems to be focused on editing feature flags, not using them in an application to toggle features. So I don't feel like my question was answered, if there is Javascript tools to support that use-case, or if it's something we would have to create for ourselves (basing our entire system on Azure components).

[HarshaNalluru]

That's good feedback @ropez. I'll check with the team and get back on the use cases.

[HarshaNalluru]

Hey @ropez,

I've created a PR that adds a sample react app with feature flags #14845.
Let me know if that helps and feel free to review the PR.

I would also expect a feature flag management system to be able to track changes and update the application (e.g. using polling or websockets subscription etc).
Is there at all a javascript client that supports these use cases, or is it something that users are expected to implement themselves?

Client doesn't offer such support, you'd have to implement yourself if your application requires so.

[HarshaNalluru]

Some more information.. the recommendation from the service team for our users would be to use App Configuration on their server-side and let the service cache and pass feature-flags to the clients.

Azure App Configuration is currently tailored to provide configuration/feature flags for server-side applications. It is possible to retrieve configuration/feature flags from a client-side application however scalability can quickly become a problem.

Azure App Configuration has a request quota detailed here.

"20,000 per hour(Once the quota is exhausted, HTTP status code 429 will be returned for all requests until the end of the hour)"

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