feature-flags-core

Core primitives for a local-first feature flag system.

This package handles:

• reading flags from .featureflags.json
• writing flag values
• evaluating flags
• optional remote flag fetch

Install

npm install feature-flags-core

Quick Usage

import { readFlags, writeFlags, getFlag } from "feature-flags-core"

writeFlags({ newUI: true, newAPI: false })

const all = readFlags()
const isNewUIEnabled = getFlag("newUI")

API

readFlags(cwd?)

Reads .featureflags.json from process.cwd() by default.

• Returns {} if the file does not exist.
• Returns {} if JSON is invalid.
• Keeps only boolean values.

writeFlags(flags, cwd?)

Writes the provided object to .featureflags.json.

getFlag(key, cwd?)

Returns true or false for one flag key.

evaluateFlags(keys, cwd?)

Returns a subset map for selected keys.

fetchRemoteFlags(url, init?)

Fetches a JSON object from a URL and normalizes it to Record<string, boolean>.

Constants and types

• FLAG_FILENAME (.featureflags.json)
• getFlagFilePath(cwd?)
• FeatureFlags
• FlagConfig

Example .featureflags.json

{
  "newUI": true,
  "newAPI": false
}