feat: add option for bootstrapping config in JS SDK (#569)

sdk/js/__tests__/Client.spec.js

@@ -56,6 +56,40 @@ describe('DevCycleClient tests', () => {
         expect(client.config).toStrictEqual(testConfig)
     })
 
+    it('should use bootstrapped config when set, not fetch a new one, initialize SDK', async () => {
+        const client = new DevCycleClient(
+            'test_sdk_key',
+            { user_id: 'user1' },
+            { bootstrapConfig: testConfig },
+        )
+        await client.onInitialized
+        expect(getConfigJson_mock).not.toBeCalled()
+        expect(client.config).toStrictEqual(testConfig)
+        expect(client.user.user_id).toEqual('user1')
+    })
+
+    it('should use bootstrapped config when set, ignore cached config', async () => {
+        getConfigJson_mock.mockImplementation(() => {
+            return Promise.resolve({ ...testConfig, cached: true })
+        })
+        const spy = jest.spyOn(window.localStorage.__proto__, 'getItem')
+        const client = new DevCycleClient('test_sdk_key', { user_id: 'user1' })
+        await client.onInitialized
+        // one call to get anon ID, one to get cached config
+        expect(spy).toHaveBeenCalledTimes(2)
+        // construct another client to test if it reads from the cache populated by the initialization of the first
+        // client
+        const client2 = new DevCycleClient(
+            'test_sdk_key',
+            { user_id: 'user1' },
+            { bootstrapConfig: testConfig },
+        )
+        await client2.onInitialized
+        // one more call to get anon ID
+        expect(spy).toHaveBeenCalledTimes(3)
+        expect(client2.config).toStrictEqual(testConfig)
+    })
+
     it('should establish a streaming connection if available', async () => {
         getConfigJson_mock.mockImplementation(() => {
             return Promise.resolve({

sdk/js/src/Client.ts

@@ -43,6 +43,7 @@ type variableEvaluatedHandler = (
 
 export type DevCycleOptionsWithDeferredInitialization = DevCycleOptions & {
     deferInitialization: true
+    bootstrapConfig?: never
 }
 
 export const isDeferredOptions = (
@@ -132,6 +133,10 @@ export class DevCycleClient<
                 throw new Error('User must be provided to initialize SDK')
             }
             this.clientInitialization(user)
+        } else if (this.options.bootstrapConfig) {
+            throw new Error(
+                'bootstrapConfig option can not be combined with deferred initialization!',
+            )
         }
 
         if (!options?.reactNative && typeof window !== 'undefined') {
@@ -171,7 +176,9 @@ export class DevCycleClient<
             storedAnonymousId,
         )
 
-        await this.getConfigCache(this.user)
+        if (!this.options.bootstrapConfig) {
+            await this.getConfigCache(this.user)
+        }
 
         // set up requestConsolidator and hook up callback methods
         this.requestConsolidator = new ConfigRequestConsolidator(
@@ -189,7 +196,15 @@ export class DevCycleClient<
         )
 
         try {
-            await this.requestConsolidator.queue(this.user)
+            if (!this.options.bootstrapConfig) {
+                await this.requestConsolidator.queue(this.user)
+            } else {
+                this.handleConfigReceived(
+                    this.options.bootstrapConfig,
+                    this.user,
+                    Date.now(),
+                )
+            }
         } catch (err) {
             this.eventEmitter.emitInitialized(false)
             this.eventEmitter.emitError(err)
@@ -727,6 +742,7 @@ export class DevCycleClient<
             user,
             this.options.configCacheTTL,
         )
+
         if (cachedConfig) {
             this.config = cachedConfig
             this.isConfigCached = true

sdk/js/src/types.ts

@@ -5,6 +5,8 @@ import {
     VariableValue,
     DVCJSON,
     DVCCustomDataJSON,
+    ConfigBody,
+    BucketedUserConfig,
 } from '@devcycle/types'
 
 export type DVCVariableValue = VariableValue
@@ -103,6 +105,14 @@ export interface DevCycleOptions {
      * Controls the maximum size the event queue can grow to until events are dropped. Defaults to `1000`.
      */
     maxEventQueueSize?: number
+
+    /**
+     * A full configuration payload to boostrap the SDK with. This will immediately initialize the SDK with
+     * the provided data and prevent a server roundtrip to fetch a new config. This option can be used for passing
+     * in a config that was prefetched in a server-side rendered environment, or to implement a custom caching
+     * system.
+     */
+    bootstrapConfig?: BucketedUserConfig
 }
 
 export interface DevCycleUser {

sdk/react/src/initializeDevCycleClient.ts

@@ -10,6 +10,7 @@ const initializeDevCycleClient = (
         return initializeDevCycle(sdkKey, {
             ...options,
             deferInitialization: true, // make typescript happy
+            bootstrapConfig: undefined,
         })
     }
     return initializeDevCycle(sdkKey, user, options)