[![React version][react-badge]][reactjs] [![TypeScript version][ts-badge]][typescript-4-7] [![Node.js version][nodejs-badge]][nodejs] [![APLv2][license-badge]][license]
npm install @harnessio/ff-react-client-sdk[![React version][react-badge]][reactjs]
[![TypeScript version][ts-badge]][typescript-4-7]
[![Node.js version][nodejs-badge]][nodejs]
[![APLv2][license-badge]][license]
Use this README to get started with our Feature Flags (FF) Client SDK for React. This guide outlines the basics of
getting started with the SDK and provides a full code sample for you to try out.
This sample doesn't include configuration options, for in depth steps and configuring the SDK, see
the React Client SDK Reference.
To use this SDK, make sure you’ve:
- Installed Node.js v12 or a newer version
- Installed React.js v16.7 or a newer version
To follow along with our test code sample, make sure you’ve:
- Created a Feature Flag on the Harness Platform
called harnessappdemodarkmode
- Created a client SDK key
and made a copy of it
The first step is to install the FF SDK as a dependency in your application. To install using npm, use:
``shell`
npm install @harnessio/ff-react-client-sdk
Or to install with yarn, use:
`shell`
yarn add @harnessio/ff-react-client-sdk
The following is a complete code example that you can use to test the harnessappdemodarkmode Flag you created on the
Harness Platform. When you run the code it will:
- Render a loading screen
- Connect to the FF service
- Retrieve all flags
- Access a flag using the useFeatureFlag hookuseFeatureFlags
- Access several flags using the hook
`typescript jsx
import React from 'react'
import ReactDOM from 'react-dom'
import {
FFContextProvider,
useFeatureFlag,
useFeatureFlags
} from '@harnessio/ff-react-client-sdk'
ReactDOM.render(
function App() {
return (
target={{
identifier: 'reactclientsdk',
name: 'ReactClientSDK'
}}
>
)
}
function SingleFeatureFlag() {
const flagValue = useFeatureFlag('harnessappdemodarkmode')
return (
The value of "harnessappdemodarkmode" is {JSON.stringify(flagValue)}
function MultipleFeatureFlags() {
const flags = useFeatureFlags()
return (
<>
Here are all our flags:
{JSON.stringify(flags, null, 2)}Async mode
By default, the React Client SDK will block rendering of children until the initial load of Feature Flags has finished, either successfully (
is emitted) or with a non-recoverable error (Event.ERROR_AUTH is emitted).
This ensures that children have immediate access to all Flags when they are rendered. However, in some circumstances it
may be beneficial to immediately render the application and handle display of loading on a component-by-component basis.
The React Client SDK's asynchronous mode allows this by passing the optional asyncMode prop when connecting with the
FFContextProvider.On Flag Not Found
The
onFlagNotFound option allows you to handle situations where a default variation is returned.
It includes the flag, variation, and whether the SDK was still initializing (loading) when the default was served.This can happen when:
1. Using
asyncMode mode without cache or initialEvaluations and where the SDK is still initializing.
2. The flag identifier is incorrect (e.g., due to a typo).
3. The Event.ERROR_AUTH event is emitted, which means that a non-recoverable error occurred, such as a wrong API key is being used or authentication failed, and the expected flags are not available for that project.`typescript jsx
target={{
identifier: 'reactclientsdk',
name: 'ReactClientSDK'
}}
onFlagNotFound={(flagNotFoundPayload, loading) => {
if (loading) {
console.debug(
Flag "${flagNotFound.flag}" not found because the SDK is still initializing. Returned default: ${flagNotFound.defaultVariation}
)
} else {
console.warn(
)
}
}}
>
By using the
prop, your application can be notified whenever a flag is missing and the default
variation has been returned.Caching evaluations
In practice flags rarely change and so it can be useful to cache the last received evaluations from the server to allow
your application to get started as fast as possible. Setting the
cache option as true or as an object (see interface
below) will allow the SDK to store its evaluations to localStorage and retrieve at startup. This lets the SDK get
started near instantly and begin serving flags, while it carries on authenticating and fetching up-to-date evaluations
from the server behind the scenes.`typescript jsx
target={{
identifier: 'reactclientsdk',
name: 'ReactClientSDK'
}}
options={{
cache: true
}}
>
`The
option can also be passed as an object with the following options.`typescript
interface CacheOptions {
// maximum age of stored cache, in ms, before it is considered stale
ttl?: number
// storage mechanism to use, conforming to the Web Storage API standard, can be either synchronous or asynchronous
// defaults to localStorage
storage?: AsyncStorage | SyncStorage
// use target attributes when deriving the cache key
// when set to false or omitted, the key will be formed using only the target identifier and SDK key
// when set to true, all target attributes with be used in addition to the target identifier and SDK key
// can be set to an array of target attributes to use a subset in addition to the target identifier and SDK key
// defaults to false
deriveKeyFromTargetAttributes?: boolean | string[]
}interface SyncStorage {
getItem: (key: string) => string | null
setItem: (key: string, value: string) => void
removeItem: (key: string) => void
}
interface AsyncStorage {
getItem: (key: string) => Promise
setItem: (key: string, value: string) => Promise
removeItem: (key: string) => Promise
}
`Overriding the internal logger
By default, the React Client SDK will log errors and debug messages using the
object. In some cases, it
can be useful to instead log to a service or silently fail without logging errors.`typescript jsx
const myLogger = {
debug: (...data) => {
// do something with the logged debug message
},
info: (...data) => {
// do something with the logged info message
},
error: (...data) => {
// do something with the logged error message
},
warn: (...data) => {
// do something with the logged warning message
}
}return (
target={{
identifier: 'reactclientsdk',
name: 'ReactClientSDK'
}}
options={{
logger: myLogger
}}
>
)
`API
$3
The
component is used to set up the React context to allow your application to access Feature Flags
using the useFeatureFlag and useFeatureFlags hooks and withFeatureFlags
HOC. At minimum, it requires the you have set up in
your Harness Feature Flags account, and the target. You can think of a target as a user.The
FFContextProvider component also accepts an options object, a fallback component, an array
of initialEvaluations, an onError handler, and can be placed in Async mode using the asyncMode
prop.
The component will be displayed while the SDK is loading and fetching your flags. The initialEvaluations
prop allows you pass an array of evaluations to use immediately as the SDK is authenticating and fetching flags.
The prop allows you to pass an event handler which will be called whenever a network error occurs.`typescript jsx
import { FFContextProvider } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
return (
apiKey="YOUR_API_KEY" // your SDK API key
target={{
identifier: 'targetId', // unique ID of the Target
name: 'Target Name', // name of the Target
attributes: { // OPTIONAL: key/value pairs of attributes of the Target
customAttribute: 'this is a custom attribute',
anotherCustomAttribute: 'this is something else'
}
}}
fallback={
Loading ...
} // OPTIONAL: component to display when the SDK is connecting
options={{ // OPTIONAL: advanced configuration options
cache: false,
baseUrl: 'https://url-to-access-flags.com',
eventUrl: 'https://url-for-events.com',
streamEnabled: true,
debug: true,
eventsSyncInterval: 60000
}}
initialEvaluations={evals} // OPTIONAL: array of evaluations to use while fetching
onError={handler} // OPTIONAL: event handler to be called on network error
>
)
}
`$3
The
hook returns a single named flag value. An optional second argument allows you to set what value
will be returned if the flag does not have a value. By default useFeatureFlag will return undefined if the flag
cannot be found.> N.B. when rendered in Async mode, the default value will be returned until the Flags are retrieved.
> Consider using the useFeatureFlagsLoading hook to determine when the SDK has finished
> loading.
`typescript jsx
import { useFeatureFlag } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
const myFlagValue = useFeatureFlag('flagIdentifier', 'default value')
return
My flag value is: {myFlagValue}
}
`$3
The
hook returns an object of Flag identifier/Flag value pairs. You can pass an array of Flag
identifiers or an object of Flag identifier/default value pairs. If an array is used and a Flag cannot be found, the
returned value for the flag will be undefined. If no arguments are passed, all Flags will be returned.> N.B. when rendered in Async mode, the default value will be returned until the Flags are retrieved.
> Consider using the useFeatureFlagsLoading hook to determine when the SDK has finished
> loading.
`typescript jsx
import { useFeatureFlag } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
const myFlagValues = useFeatureFlags()
return (
<>
My flag values are:
{JSON.stringify(myFlagValues, null, 2)}
)
}
`#### Get a subset of Flags
typescript jsx
const myFlagValues = useFeatureFlags(['flag1', 'flag2'])
`#### Get a subset of Flags with custom default values
typescript jsx
const myFlagValues = useFeatureFlags({
flag1: 'defaultForFlag1',
flag2: 'defaultForFlag2'
})
`$3
The
hook returns a boolean value indicating whether the SDK is currently loading Flags
from the server.`typescript jsx
import {
useFeatureFlagsLoading,
useFeatureFlags
} from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
const isLoading = useFeatureFlagsLoading()
const flags = useFeatureFlags()
if (isLoading) {
return
Loading ...
} return (
<>
My flag values are:
{JSON.stringify(flags, null, 2)}
)
}
`$3
The React Client SDK internally uses the Javascript Client SDK to communicate with Harness. Sometimes it might be useful
to be able to access the instance of the Javascript Client SDK rather than use the existing hooks or higher-order
components (HOCs). The
hook returns the current Javascript Client SDK instance that the React
Client SDK is using. This instance will be configured, initialized and have been hooked up to the various events the
Javascript Client SDK provides.`typescript jsx
import {
useFeatureFlagsClient,
useFeatureFlagsLoading
} from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
const client = useFeatureFlagsClient()
const loading = useFeatureFlagsLoading()
if (loading || !client) {
return
Loading...
} return (
My flag value is: {client.variation('flagIdentifier', 'default value')}
)
}
`$3
The
higher-order component (HOC) wraps your component and conditionally renders only when the named flag
is enabled or matches a specific value.`typescript jsx
import { ifFeatureFlag } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
return
This should render if the flag is on
}const MyConditionalComponent = ifFeatureFlag('flag1')(MyComponent)
`You can then use
as a normal component, and only render if flag1's value is truthy.#### Conditionally with a specific value
`typescript jsx
import { ifFeatureFlag } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
return
This should render if the flag evaluates to 'ABC123'
}const MyConditionalComponent = ifFeatureFlag('flag1', { matchValue: 'ABC123' })(
MyComponent
)
`You can then use
as a normal component, only render if flag1's value matches the passed
condition.#### Loading fallback when in async mode
If Async mode is used, by default the component will wait for Flags to be retrieved before showing. This
behaviour can be overridden by passing an element as
loadingFallback; when loading the loadingFallback will be
displayed until the Flags are retrieved, at which point the component will either show or hide as normal.`typescript jsx
import { ifFeatureFlag } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent() {
return
This should render if the flag is on
}const MyConditionalComponent = ifFeatureFlag('flag1', {
loadingFallback:
Loading...
})(MyComponent)
`$3
The
higher-order component (HOC) wraps your component and adds flags and loading as additional
props. flags contains the evaluations for all known flags and loading indicates whether the SDK is actively fetching
Flags.`typescript jsx
import { withFeatureFlags } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent({ flags }) {
return
Flag1's value is {flags.flag1}
}const MyComponentWithFlags = withFeatureFlags(MyComponent)
`#### Loading in async mode
If Async mode is used, the
prop will indicate whether the SDK has finished the initial load of Feature Flags.
When loading finishes, either successfully (Event.READY is emitted) or with a non-recoverable error (Event.ERROR_AUTH is emitted), the loading prop will be false and the flags prop will contain all known Flags.`typescript jsx
import { withFeatureFlags } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent({ flags, loading }) {
if (loading) {
return
Loading...
} return
Flag1's value is {flags.flag1}
}const MyComponentWithFlags = withFeatureFlags(MyComponent)
`$3
The React Client SDK internally uses the Javascript Client SDK to communicate with Harness. Sometimes it might be useful
to be able to access the instance of the Javascript Client SDK rather than use the existing hooks or higher-order
components (HOCs). The
HOC wraps your component and adds featureFlagsClient as additional
prop. featureFlagsClient is the current Javascript Client SDK instance that the React Client SDK is using. This
instance will be configured, initialized and have been hooked up to the various events the Javascript Client SDK
provides.`typescript jsx
import { withFeatureFlagsClient } from '@harnessio/ff-react-client-sdk'// ...
function MyComponent({ featureFlagsClient }) {
if (featureFlagsClient) {
return (
Flag1's value is {featureFlagsClient.variation('flag1', 'no value')}
)
} return
The Feature Flags client is not currently available
}const MyComponentWithClient = withFeatureFlagsClient(MyComponent)
`Testing with Jest
When running tests with Jest, you may want to mock the SDK to avoid making network requests. You can do this by using
the included
component. This component accepts a listing of flags and their values, and will mock the SDK
to return those values. In the example below, we use Testing Library to render the component that
internally uses the useFeatureFlag hook.> N.B. to use the
TestWrapper component, you must import it from the dist/cjs/test-utils directory, not from the
> main package.`typescript jsx
import { render, screen } from '@testing-library/react'
import { TestWrapper } from '@harnessio/ff-react-client-sdk/dist/cjs/test-utils'// ...
test('it should render the flag value', () => {
render(
)
expect(screen.getByText('value1')).toBeInTheDocument()
})
``For further examples and config options, see
the React.js Client SDK Reference
For more information about Feature Flags, see
our Feature Flags documentation.
[ts-badge]: https://img.shields.io/badge/TypeScript-4.7-blue.svg
[react-badge]: https://img.shields.io/badge/React.js->=%2016.7-blue.svg
[nodejs-badge]: https://img.shields.io/badge/Node.js->=%2012-blue.svg
[nodejs]: https://nodejs.org/dist/latest/docs/api/
[reactjs]: https://reactjs.org
[typescript-4-7]: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-7.html
[license-badge]: https://img.shields.io/badge/license-APLv2-blue.svg
[license]: https://github.com/drone/ff-nodejs-server-sdk/blob/main/LICENSE
[jest]: https://facebook.github.io/jest/
[eslint]: https://github.com/eslint/eslint
[prettier]: https://prettier.io