Examples for Microsoft Feature Management for JavaScript

These examples show how to use the Microsoft Feature Management in an express application.

Prerequisites

The examples are compatible with LTS versions of Node.js.

Setup & Run

1. Install the dependencies using npm:

   npm install

2. Run the examples:

   node server.mjs

3. Visit http://localhost:3000/Beta and use userId and groups query to specify the targeting context (e.g. /Beta?userId=Jeff or /Beta?groups=Admin).

   • If you are not targeted, you will get the message "Page not found".

   • If you are targeted, you will get the message "Welcome to the Beta page!".

Targeting

The targeting mechanism uses the exampleTargetingContextAccessor to extract the targeting context from the request. This function retrieves the userId and groups from the query parameters of the request.

const exampleTargetingContextAccessor = {
    getTargetingContext: () => {
        const req = requestAccessor.getStore();
        if (req === undefined) {
            return undefined;
        }
        // read user and groups from request query data
        const { userId, groups } = req.query;
        // return aa ITargetingContext with the appropriate user info
        return { userId: userId, groups: groups ? groups.split(",") : [] };
    }
};

The FeatureManager is configured with this targeting context accessor:

const featureManager = new FeatureManager(
    featureProvider, 
    { 
        targetingContextAccessor: exampleTargetingContextAccessor 
    }
);

This allows you to get ambient targeting context while doing feature flag evaluation.

Request Accessor

The requestAccessor is an instance of AsyncLocalStorage from the async_hooks module. It is used to store the request object in asynchronous local storage, allowing it to be accessed throughout the lifetime of the request. This is particularly useful for accessing request-specific data in asynchronous operations. For more information, please go to https://nodejs.org/api/async_context.html

import { AsyncLocalStorage } from "async_hooks";
const requestAccessor = new AsyncLocalStorage();

Middleware is used to store the request object in the AsyncLocalStorage:

server.use((req, res, next) => {
    requestAccessor.run(req, next);
});