FlagwardOverview
The JavaScript SDKs — one shared core, one thin adapter per framework.
Flagward's JavaScript SDKs are one shared core and one thin adapter per framework.
| Package | npm | What it is |
|---|---|---|
@flagward/core | @flagward/core | The client, the rule evaluator, and console reporting. No framework assumptions beyond the browser APIs it guards. |
@flagward/react | @flagward/react | The React adapter: a provider, useFlag and useFlags. |
@flagward/vue | @flagward/vue | The Vue adapter: a plugin, useFlag and useFlags. |
@flagward/solid | @flagward/solid | The Solid adapter: a provider, useFlag and useFlags. |
@flagward/svelte | @flagward/svelte | The Svelte adapter: setFlagward, useFlag and useFlags, built on svelte/store. |
Every adapter re-exports @flagward/core, so installing the adapter for your
framework is enough — you never need both.
Installing
npm install @flagward/reactWhy a shared core
The client, the rule evaluator, the logger, and the types have no framework imports at all — a framework adapter is a provider and two or three bindings on top of them. The evaluator exists once, and every adapter depends on it, so the same user, the same flag, and the same server are answered the same way regardless of which framework asked.
How evaluation works
An SDK downloads the full set of flags and their targeting rules for the
environment your API key belongs to, then evaluates each flag locally, in
your process. Rules are evaluated against a context you supply — user
attributes such as plan, country, or id — under AND or OR, tried in
priority order; the first match wins. Supported operators: EQUALS,
NOT_EQUALS, GREATER_THAN, LESS_THAN, IN_LIST, CONTAINS.
getFlag/useFlag never throw. A flag that is not in the environment reads
as undefined, so your own fallback decides what happens, and the reason is
reported to the console once.
Live updates
Every adapter opens a Server-Sent Events stream and keeps the local snapshot in step with the server:
- A flag changed on the server reaches every component within a second.
- Coming back online re-reads the flags — a dropped connection means missed events, so reconnecting alone would serve a stale value indefinitely.
- Returning to a backgrounded tab does the same, since a machine waking from sleep drops its connection without the browser ever reporting the network as gone.
- Where there is no
EventSource— server rendering, React Native, plain Node — live updates are reported as off and the SDK keeps serving the flags it already read.
A failure never propagates into your application: flags keep their last known values, and your own fallback decides what the user sees.
Error reporting
Every failure an SDK recovers from is reported once per page load, prefixed
with [Flagward]. logLevel narrows it:
| Value | Reports |
|---|---|
"warn" (default) | everything: unknown flags, dropped streams, network failures |
"error" | only what cannot work at all: a missing or rejected API key, a missing provider |
"silent" | nothing |
Self-hosting
host is optional on every SDK and defaults to the hosted service at
https://app.flagward.com. A self-hosted install passes its own — see
Self-hosting.
Registration
Each adapter names itself when it registers with the server (the core as
JAVASCRIPT, and the adapters as REACT, VUE, SOLID, SVELTE), so the
dashboard shows what the application actually installed.
Module format
Every package ships ESM only, with type declarations. There is no CommonJS build.