backstage/docs/reference/createPlugin-feature-flags.md

createPlugin - feature flags

The featureFlags object passed to the register function makes it possible for plugins to register Feature Flags in Backstage for users to opt into. You can use this to split out logic in your code for manual A/B testing, etc.

export type FeatureFlagsHooks = {
  register(name: FeatureFlagName): void;
};

Here's a code sample:

import { createPlugin } from '@backstage/core';

export default createPlugin({
  id: 'welcome',
  register({ router, featureFlags }) {
    // router.registerRoute('/', Component);
    featureFlags.register('enable-example-feature');
  },
});

Using with useApi

To use it, you'll first need to register the FeatureFlags API via ApiRegistry in your apis.ts in your App:

import {
  ApiHolder,
  ApiRegistry,
  featureFlagsApiRef,
  FeatureFlags,
} from '@backstage/core';

const builder = ApiRegistry.builder();
builder.add(featureFlagsApiRef, new FeatureFlags());

export default builder.build() as ApiHolder;

Then, later, you can directly use it via useApi:

import React, { FC } from 'react';
import { Button } from '@material-ui/core';
import { FeatureFlagState, featureFlagsApiRef, useApi } from '@backstage/core';

const ExampleButton: FC<{}> = () => {
  const flags = useApi(featureFlagsApiRef).getFlags();

  const handleClick = () => {
    flags.set('enable-example-feature', FeatureFlagState.On);
  };

  return (
    <Button variant="contained" color="primary" onClick={handleClick}>
      Enable the 'enable-example-feature' feature flag
    </Button>
  );
};