reecelucas · March 28, 2020 15:15 · Mar 28, 2020 · Mar 27, 2020 · Mar 27, 2020 · Mar 26, 2020
diff --git a/usage-server.js b/usage-server.js
@@ -6,17 +6,30 @@ const app = express();
 
 const { isFeatureEnabled, getFeatureConfig } = getFeatureUtils({
   environment: "development",
-  cookieName: "featureOverrides"
+  cookieName: "featureOverrides",
 });
 
+const ensureFeatureUtils = (req, _res, next) => {
+  if (!req.cookies) {
+    throw new Error(
+      "Server configuration error: ensureFeatureUtils middleware requires cookie-parser middleware upstream"
+    );
+  }
+
+  const { featureOverrides } = req.cookies;
+
+  req.isFeatureEnabled = (featureName) => isFeatureEnabled(featureName, featureOverrides);
+  req.getFeatureConfig = () => getFeatureConfig(featureOverrides);
+  next();
+};
+
 app.use(cookieParser());
+app.use(ensureFeatureUtils);
 
 app.get("/", (req, res) => {
-  const featureOverrides = req.cookies.featureOverrides;
-
-  console.log(getFeatureConfig(featureOverrides)); // { FEATURE_A: true, FEATURE_B: false }
+  console.log(req.getFeatureConfig()); // { FEATURE_A: true, FEATURE_B: false }
 
-  if (isFeatureEnabled("FEATURE_A", featureOverrides)) {
+  if (req.isFeatureEnabled("FEATURE_A")) {
     res.send("FEATURE_A is enabled");
   } else {
     res.send("FEATURE_A is NOT enabled");

diff --git a/featureFlags.js b/featureFlags.js
@@ -42,7 +42,7 @@ export const getFeatureUtils = ({ environment, cookieName }) => {
     const config = getConfig(environment, cookieValue);
     const value = config[featureName];
 
-    if (!value) {
+    if (value === undefined) {
       throw new Error(
         `${featureName} is not defined for the ${environment} environment`
       );
@@ -51,8 +51,7 @@ export const getFeatureUtils = ({ environment, cookieName }) => {
     return value;
   };
 
-  // `values` should be an object, E.g. { FEATURE_A: false }.
-  // This function could be called on a feature-flipper UI to set features for local development.
+  // `values` should be an object. E.g. setFeatureOverrides({ FEATURE_A: false })
   const setFeatureOverrides = values => {
     Cookies.set(cookieName, values);
   };

diff --git a/usage-client.js b/usage-client.js
@@ -12,7 +12,7 @@ const {
 console.log(isFeatureEnabled("FEATURE_B")); // false
 console.log(getFeatureConfig()); // { FEATURE_A: true, FEATURE_B: false }
 
-setFeatureOverrides("featureOverrides", { FEATURE_B: true });
+setFeatureOverrides({ FEATURE_B: true });
 
 // After refreshing page...
 console.log(isFeatureEnabled("FEATURE_B")); // true

diff --git a/featureFlags.js b/featureFlags.js
@@ -59,7 +59,7 @@ export const getFeatureUtils = ({ environment, cookieName }) => {
 
   const getFeatureConfig = cookieString => {
     const cookieValue = cookieString || cookieValueFromDocument;
-    return getConfig(environment, cookieString);
+    return getConfig(environment, cookieValue);
   };
 
   return { isFeatureEnabled, setFeatureOverrides, getFeatureConfig };

diff --git a/featureFlags.js b/featureFlags.js
@@ -10,19 +10,19 @@ const getDefaultConfigForEnv = environment =>
     {}
   );
 
-const getConfigOverridesFromCookie = cookieValue => {
+const getConfigOverridesFromCookie = cookieString => {
   try {
-    return cookieValue ? JSON.parse(cookieValue) : {};
+    return cookieString ? JSON.parse(cookieString) : {};
   } catch (error) {
     throw new Error(
       "Could not determine feature config overrides: error parsing cookie value"
     );
   }
 };
 
-const getConfig = (environment, cookieValue) => {
+const getConfig = (environment, cookieString) => {
   const defaultConfig = getDefaultConfigForEnv(environment);
-  const overrides = getConfigOverridesFromCookie(cookieValue);
+  const overrides = getConfigOverridesFromCookie(cookieString);
 
   return {
     ...defaultConfig,
@@ -39,7 +39,7 @@ export const getFeatureUtils = ({ environment, cookieName }) => {
     // be accessed on the `request` object. On the client we retrieve the cookie value from
     // the document.
     const cookieValue = cookieString || cookieValueFromDocument;
-    const config = getConfig(environment, cookieString);
+    const config = getConfig(environment, cookieValue);
     const value = config[featureName];
 
     if (!value) {
@@ -62,5 +62,5 @@ export const getFeatureUtils = ({ environment, cookieName }) => {
     return getConfig(environment, cookieString);
   };
 
-  return { isFeatureEnabled, getFeatureConfig, setFeatureOverrides };
+  return { isFeatureEnabled, setFeatureOverrides, getFeatureConfig };
 };
diff --git a/featureConfig.js b/featureConfig.js
@@ -0,0 +1,19 @@
+export default {
+  FEATURE_A: {
+    name: 'FEATURE_A',
+    description: 'Human readable description of feature A',
+    enabled: {
+      development: true,
+      production: false
+    }
+  },
+  FEATURE_B: {
+    name: 'FEATURE_B',
+    description: 'Human readable description of feature B',
+    enabled: {
+      development: false,
+      production: true
+    }
+  }
+};
+
diff --git a/featureFlags.js b/featureFlags.js
@@ -0,0 +1,66 @@
+import config from "./featureConfig";
+import Cookies from "js-cookie";
+
+const getDefaultConfigForEnv = environment =>
+  Object.entries(config).reduce(
+    (obj, [key, value]) => ({
+      ...obj,
+      [key]: value.enabled[environment]
+    }),
+    {}
+  );
+
+const getConfigOverridesFromCookie = cookieValue => {
+  try {
+    return cookieValue ? JSON.parse(cookieValue) : {};
+  } catch (error) {
+    throw new Error(
+      "Could not determine feature config overrides: error parsing cookie value"
+    );
+  }
+};
+
+const getConfig = (environment, cookieValue) => {
+  const defaultConfig = getDefaultConfigForEnv(environment);
+  const overrides = getConfigOverridesFromCookie(cookieValue);
+
+  return {
+    ...defaultConfig,
+    ...overrides
+  };
+};
+
+export const getFeatureUtils = ({ environment, cookieName }) => {
+  const cookieValueFromDocument = Cookies.get(cookieName);
+
+  const isFeatureEnabled = (featureName, cookieString) => {
+    // If `cookieString` is provided we use this to determine feature overrides.
+    // This is useful when using `isFeatureEnabled` on the server, where `cookieName` can
+    // be accessed on the `request` object. On the client we retrieve the cookie value from
+    // the document.
+    const cookieValue = cookieString || cookieValueFromDocument;
+    const config = getConfig(environment, cookieString);
+    const value = config[featureName];
+
+    if (!value) {
+      throw new Error(
+        `${featureName} is not defined for the ${environment} environment`
+      );
+    }
+
+    return value;
+  };
+
+  // `values` should be an object, E.g. { FEATURE_A: false }.
+  // This function could be called on a feature-flipper UI to set features for local development.
+  const setFeatureOverrides = values => {
+    Cookies.set(cookieName, values);
+  };
+
+  const getFeatureConfig = cookieString => {
+    const cookieValue = cookieString || cookieValueFromDocument;
+    return getConfig(environment, cookieString);
+  };
+
+  return { isFeatureEnabled, getFeatureConfig, setFeatureOverrides };
+};
diff --git a/usage-client.js b/usage-client.js
@@ -0,0 +1,19 @@
+import { getFeatureUtils } from "./featureFlags";
+
+const {
+  isFeatureEnabled,
+  getFeatureConfig,
+  setFeatureOverrides
+} = getFeatureUtils({
+  environment: "development",
+  cookieName: "featureOverrides"
+});
+
+console.log(isFeatureEnabled("FEATURE_B")); // false
+console.log(getFeatureConfig()); // { FEATURE_A: true, FEATURE_B: false }
+
+setFeatureOverrides("featureOverrides", { FEATURE_B: true });
+
+// After refreshing page...
+console.log(isFeatureEnabled("FEATURE_B")); // true
+console.log(getFeatureConfig()); // { FEATURE_A: true, FEATURE_B: true }
diff --git a/usage-server.js b/usage-server.js
@@ -0,0 +1,24 @@
+import express from "express";
+import cookieParser from "cookie-parser";
+import { getFeatureUtils } from "./featureFlags";
+
+const app = express();
+
+const { isFeatureEnabled, getFeatureConfig } = getFeatureUtils({
+  environment: "development",
+  cookieName: "featureOverrides"
+});
+
+app.use(cookieParser());
+
+app.get("/", (req, res) => {
+  const featureOverrides = req.cookies.featureOverrides;
+
+  console.log(getFeatureConfig(featureOverrides)); // { FEATURE_A: true, FEATURE_B: false }
+
+  if (isFeatureEnabled("FEATURE_A", featureOverrides)) {
+    res.send("FEATURE_A is enabled");
+  } else {
+    res.send("FEATURE_A is NOT enabled");
+  }
+});
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