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Install the Latest Version

npm install @prefab-cloud/prefab-cloud-node

Initialize a Client

import { Prefab } from "@prefab-cloud/prefab-cloud-node";

if (!process.env.PREFAB_API_KEY) {
throw new Error("PREFAB_API_KEY is not set");

const prefab = new Prefab({
apiKey: process.env.PREFAB_API_KEY,
enableSSE: true,
defaultLogLevel: "warn",

await prefab.init();

Feature Flags and Dynamic Config

After the init completes you can use

  • prefab.isFeatureEnabled('') returns true or false
  • prefab.get('') returns a raw value


Prefab supports context for intelligent rule-based evaluation of get and isFeatureEnabled based on the current request/device/user/etc.


const context = {
user: { key: "some-unique-identifier", country: "US" },
subscription: { key: "pro-sub", plan: "pro" },

You can pass this in to each call

  • prefab.get('', context, defaultValue)
  • prefab.isFeatureEnabled('', context, false)

Or you can set the context in a block (perhaps surrounding evaluation of a web request)

prefab.inContext(context, (pf) => {
const optionalJustInTimeContext = { ... }

console.log(pf.get("", optionalJustInTimeContext, defaultValue))
console.log(pf.isEnabled("", optionalJustInTimeContext, false))

Dynamic Logging

The node ecosystem has a vast landscape of logging libraries. Rather than making an opinionated choice about which logger you should use, Prefab provides both a simple console.log wrapper and a way to integrate with your existing logger.

If you're logging to STDOUT (e.g. console.log) we provide prefab.logger for convenience.

// Provide a meaningful logger name and default level
const logger = prefab.logger("", "warn");

// simple info logging`getting results for ${userId}`);

You can provide the context to the logger as well (for evaluating dynamic log level rules)
"doing something complicated...",
{ user: { key: userId } },

Or, using the inContext block:

const prefabContext = { user: { key: userId } };

// ... later in your code
prefab.inContext(prefabContext, (prefab) => {
const logger = prefab.logger("", "warn");`doing something complicated...`);


Option Definitions

collectEvaluationSummariesSend counts of config/flag evaluation results back to Prefab to view in web apptrue
collectLoggerCountsSend counts of logger usage back to Prefab to power log-levels configuration screentrue
contextUploadModeUpload either context "shapes" (the names and data types your app uses in prefab contexts) or periodically send full example contexts"periodicExample"
defaultLevelLevel to be used as the min-verbosity for a loggerPath if no value is configured in Prefab"warn"
enableSSEWhether or not we should listen for live changes from Prefabtrue
enablePollingWhether or not we should poll for changes from Prefabfalse