update

Author: zhiyuanliang-ms

examples/express-app/README.md

@@ -0,0 +1,69 @@
+# 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](https://github.com/nodejs/release#release-schedule).
+
+## Setup & Run
+
+1. Install the dependencies using `npm`:
+
+    ```bash
+    npm install
+    ```
+    
+1. Run the examples:
+
+    ```bash
+    node server.mjs
+    ```
+
+1. 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.
+
+```javascript
+const exampleTargetingContextAccessor = () => {
+    const req = requestAccessor.getStore();
+    const { userId, groups } = req.query;
+    return { userId: userId, groups: groups ? groups.split(",") : [] };
+};
+```
+
+The `FeatureManager` is configured with this targeting context accessor:
+
+```javascript
+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
+
+```javascript
+import { AsyncLocalStorage } from "async_hooks";
+const requestAccessor = new AsyncLocalStorage();
+```
+
+Middleware is used to store the request object in the AsyncLocalStorage:
+
+```javascript
+server.use((req, res, next) => {
+    requestAccessor.run(req, next);
+});
+```

examples/express-app/server.mjs

@@ -11,9 +11,9 @@ const featureProvider = new ConfigurationObjectFeatureFlagProvider(config);
 
 // https://nodejs.org/api/async_context.html
 import { AsyncLocalStorage } from "async_hooks";
-const asyncLocalStorage = new AsyncLocalStorage();
+const requestAccessor = new AsyncLocalStorage();
 const exampleTargetingContextAccessor = () => {
-    const req = asyncLocalStorage.getStore();
+    const req = requestAccessor.getStore();
     const { userId, groups } = req.query;
     return { userId: userId, groups: groups ? groups.split(",") : [] };
 };
@@ -31,11 +31,11 @@ const PORT = 3000;
 
 // Use a middleware to store the request object in async local storage.
 // The async local storage allows the targeting context accessor to access the current request throughout its lifetime.
-// Middleware 1
+// Middleware 1 (request object is stored in async local storage here and it will be available across the following chained async operations)
 //   Middleware 2
-//     Request Handler (feature flag evaluation)
+//     Request Handler (feature flag evaluation happens here)
 server.use((req, res, next) => {
-    asyncLocalStorage.run(req, next);
+    requestAccessor.run(req, next);
 });
 
 server.get("/", (req, res) => {