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Node

Install the Latest Version

npm install @prefab-cloud/prefab-cloud-node
yarn add @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('some.feature.name') returns true or false
  • prefab.get('some.config.name') returns a raw value

Context

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

Given

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('some.config.name', context, defaultValue)
  • prefab.isFeatureEnabled('some.feature.name', 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("some.config.name", optionalJustInTimeContext, defaultValue))
  console.log(pf.isEnabled("some.config.name", 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("express.example.app.users-path", "warn");

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

You can provide the context to the logger as well (for evaluating dynamic log level rules)

logger.info(
  "express.example.app.users-path",
  "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("express.example.app.users-path", "warn");

  logger.info(`doing something complicated...`);
});

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

You can use this to wrap your existing logging calls. Example:

const defaultLevel = "warn";

myLogger.info = (loggerName, msg, context) => {
  if (
    prefab.shouldLog({
      loggerName,
      defaultLevel,
      desiredLevel: "info",
      contexts: context,
    })
  ) {
    // Now you call the underlying method on your preferred logger
    myPreferredLoggerLibrary.info(msg);
  }
};

// repeat for debug, warn, error, etc.

Example invocation:

myLogger.info(
  "express.example.app.users-path",
  "doing something complicated...",
  { user: { key: userId } },
);

Or, using the inContext block:

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

// ... later in your code
prefab.inContext(prefabContext, (prefab) => {
  myLogger.info(
    "express.example.app.users-path",
    "doing something complicated",
  );
});

Reference

Option Definitions

Name Description Default
collectEvaluationSummaries Send counts of config/flag evaluation results back to Prefab to view in web app true
collectLoggerCounts Send counts of logger usage back to Prefab to power log-levels configuration screen true
contextUploadMode Upload either context "shapes" (the names and data types your app uses in prefab contexts) or periodically send full example contexts "periodicExample"
defaultLevel Level to be used as the min-verbosity for a loggerPath if no value is configured in Prefab "warn"
enableSSE Whether or not we should listen for live changes from Prefab true
enablePolling Whether or not we should poll for changes from Prefab false