chore: Improve docs and add circleci config

Author: kevin-greene-ck

.circleci/config.yml

@@ -0,0 +1,99 @@
+defaults: &defaults
+  working_directory: ~/dynamic-config
+  docker:
+    - image: circleci/node:8.9.4
+
+version: 2
+executorType: machine
+jobs:
+  test_node_6:
+    <<: *defaults
+    docker:
+      - image: circleci/node:6.12.3
+    steps:
+      - checkout
+      - run:
+          name: Install NPM Dependencies
+          command: npm install
+      - run:
+          name: Run Test Suite
+          command: npm test
+
+  test_node_8:
+    <<: *defaults
+    steps:
+      - checkout
+      - run:
+          name: Install NPM Dependencies
+          command: npm install
+      - run:
+          name: Run Test Suite
+          command: npm test
+
+  publish:
+    <<: *defaults
+    steps:
+      - checkout
+      - run:
+          name: Generate .npmrc File
+          command: 'echo "//registry.npmjs.org/:_authToken=${NPM_TOKEN}" > ~/.npmrc'
+      - run:
+          name: Install NPM Dependencies
+          command: npm install
+      - run:
+          name: Build Publish Assets
+          command: npm run build
+      - run:
+          name: Publish to NPM
+          command: npm publish --access public
+
+  publish_next:
+    <<: *defaults
+    steps:
+      - checkout
+      - run:
+          name: Generate .npmrc File
+          command: 'echo "//registry.npmjs.org/:_authToken=${NPM_TOKEN}" > ~/.npmrc'
+      - run:
+          name: Install NPM Dependencies
+          command: npm install
+      - run:
+          name: Build Publish Assets
+          command: npm run build
+      - run:
+          name: Publish to NPM
+          command: npm publish --tag next --access public
+
+workflows:
+  version: 2
+  build_publish:
+      jobs:
+        - test_node_6:
+            filters:
+              tags:
+                only: /.*/
+
+        - test_node_8:
+            filters:
+              tags:
+                only: /.*/
+
+        - publish:
+            requires:
+              - test_node_6
+              - test_node_8
+            filters:
+              tags:
+                only: /^(v){1}[0-9]+(\.[0-9]+){2}$/
+              branches:
+                ignore: /.*/
+
+        - publish_next:
+            requires:
+              - test_node_6
+              - test_node_8
+            filters:
+              tags:
+                only: /^(v){1}[0-9]+(\.[0-9]+){2}(-)[0-9]+$/
+              branches:
+                ignore: /.*/

README.md

@@ -4,6 +4,10 @@ A dynamic feature flags library for Node.js. This library gives you fine-grained
 
 This implementation is largely based on [Feature Toggles](https://twitter.github.io/finagle/guide/Configuration.html#feature-toggles) in [Twitter's Finagle framework](https://github.com/twitter/finagle).
 
+For a detail looks at feature flags check out this article [Feature Toggles](https://martinfowler.com/articles/feature-toggles.html).
+
+The idea behind feature flags is that they give you a way for testing new code and ramping that code over time. In your configuration you would provide a description of what percentage of requests should use a particular code path and the library will somewhat randomly return a boolean for each toggle representing if it should be used on a particular request or not. Once a code path is ramped to 100% it is expected the feature flag for that code would be removed.
+
 ## Install
 
 This feature flags library has a peer dependency on `@creditkarma/dynamic-config`.
@@ -15,9 +19,51 @@ $ npm install --save @creditkarma/feature-flags
 
 ## Usage
 
+Using feature flags is very easy. They are really just a boolean indicating which code path you should use.
+
+```typescript
+import { toggleMap, Toggle } from '@creditkarma/feature-flags'
+
+async function startApp(app) {
+    const toggle: Toggle = await toggleMap('com.example.service.UseNewBackend')
+
+    app.get('/test', (req, res) => {
+        if (toggle()) {
+            // Use new code path
+        } else {
+            // Use old code path
+        }
+    })
+}
+```
+
+In application code there are only two things you need to use. The `toggleMap` function and the `Toggle` type.
+
+### `toggleMap`
+
+The `toggleMap` is a function that returns a Promise of a toggle for a given key. Your application can have many toggles. Each of these toggles has a unique string identifier that you specify. You provide this id to the `toggleMap` function and it gives you back a `Promise<Toggle>`. A `Toggle` is a function that just returns a `boolean`. It will return, randomly, `true` based on the configured percentage.
+
+## Configuration
+
+The real work of the feature flag is actually the configuration. In your application config you would have a key call `toggles`. This key is expected to be at the root level of your config `JSON`:
+
+```json
+{
+    "toggles": [
+        {
+            "id": "com.example.service.UseNewBackend",
+            "description": "Use new backend code",
+            "fraction": 0.1,
+        }
+    ]
+}
+```
+
 ### Dynamic Config
 
-[DynamicConfig](https://github.com/creditkarma/dynamic-config) is a pluggable config library for Node.js that allows for runtime changes to config values.
+[DynamicConfig](https://github.com/creditkarma/dynamic-config) is a pluggable config library for Node.js that allows for runtime changes to config values. This is the basis for our feature flags support. It certainly isn't required that you use Dyanmic Config for all of your application config, but that would be recommended.
+
+
 
 ### Flag Schema
 
@@ -53,15 +99,3 @@ $ npm install --save @creditkarma/feature-flags
     "required": [ "toggles" ]
 }
 ```
-
-```json
-{
-    "toggles": [
-        {
-            "id": "com.example.service.UseNewBackend",
-            "description": "Use new backend code",
-            "fraction": 0.1,
-        }
-    ]
-}
-```

src/main/toggles.ts

@@ -1,18 +1,18 @@
 import { config } from '@creditkarma/dynamic-config'
 import * as logger from './logger'
 import { DEFAULT_TOGGLES_PATH } from './constants'
-import { objectMatchesSchema } from './utils'
+import { objectMatchesSchema, memoize } from './utils'
 import { toggleSchema } from './schema'
 import {
-    DescMap,
+    ToggleMap,
     IToggleDescription,
     Toggle,
 } from './types'
 
-const rawToggles: DescMap = new Map()
+const rawToggles: ToggleMap = new Map()
 
-const futureToggles: Promise<DescMap> =
-    new Promise((resolve, reject) => {
+const lazyToggles: () => Promise<ToggleMap> = memoize(() => {
+    return new Promise((resolve, reject) => {
         config().watch<Array<IToggleDescription>>(DEFAULT_TOGGLES_PATH).onValue((toggles): void => {
             if (objectMatchesSchema(toggleSchema, { toggles })) {
                 toggles.forEach((next: IToggleDescription) => {
@@ -27,12 +27,13 @@ const futureToggles: Promise<DescMap> =
             }
         })
     })
+})
 
-export function ToggleMap(key: string): Promise<Toggle> {
-    return futureToggles.then((map: DescMap) => {
+export function toggleMap(key: string): Promise<Toggle> {
+    return lazyToggles().then((map: ToggleMap) => {
         return () => {
-            if (rawToggles.has(key)) {
-                const toggleDesc: IToggleDescription = rawToggles.get(key)!
+            if (map.has(key)) {
+                const toggleDesc: IToggleDescription = map.get(key)!
                 const randomInt: number = Math.random()
                 return (randomInt < toggleDesc.fraction)
 

src/main/types.ts

@@ -1,4 +1,4 @@
-export type DescMap = Map<string, IToggleDescription>
+export type ToggleMap = Map<string, IToggleDescription>
 
 export interface IToggleDescription {
     id: string

src/main/utils.ts

@@ -4,4 +4,18 @@ const JSON_VALIDATOR: JsonValidator.Ajv = new JsonValidator()
 
 export function objectMatchesSchema(schema: object, data: any): boolean {
     return JSON_VALIDATOR.validate(schema, data) as boolean
+}
+
+export function memoize<T>(fn: () => T): () => T {
+    let cachedValue: any = undefined
+
+    return (): T => {
+        if (cachedValue !== undefined) {
+            return cachedValue
+
+        } else {
+            cachedValue = fn()
+            return cachedValue
+        }
+    }
 }

src/tests/integration/index.spec.ts

@@ -1,7 +1,7 @@
 import { expect } from 'code'
 import * as Lab from 'lab'
 
-import { ToggleMap } from '../../main'
+import { toggleMap } from '../../main'
 
 export const lab = Lab.script()
 
@@ -10,12 +10,12 @@ const it = lab.it
 
 describe('ToggleMap', () => {
     it('should return false for toggle set to 0.0', async () => {
-        const toggle = await ToggleMap('com.creditkarma.featureFlags.AlwaysDisabled')
+        const toggle = await toggleMap('com.creditkarma.featureFlags.AlwaysDisabled')
         expect(toggle()).to.equal(false)
     })
 
     it('should return true for toggle set to 1.0', async () => {
-        const toggle = await ToggleMap('com.creditkarma.featureFlags.AlwaysEnabled')
+        const toggle = await toggleMap('com.creditkarma.featureFlags.AlwaysEnabled')
         expect(toggle()).to.equal(true)
     })
 })