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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 = new Map([
new Map([
["key", "some-unique-identifier"],
["country", "US"],

new Map([
["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

prefab.shouldLog(loggerName, desiredLevel, defaultLevel, contexts) returns true or false


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