What is react-test-renderer?
The react-test-renderer package is designed for testing React components in a more efficient and lightweight manner. It provides a renderer that can be used to render React components into pure JavaScript objects without depending on the DOM or a native mobile environment. This makes it ideal for testing components in isolation from the browser or any other external environment.
What are react-test-renderer's main functionalities?
Rendering components to JSON
This feature allows you to render a React component and generate a JSON output of the rendered component. This is useful for snapshot testing, where you can compare the current version of the component with a previously stored snapshot.
import React from 'react';
import renderer from 'react-test-renderer';
const component = renderer.create(<MyComponent />);
let tree = component.toJSON();
expect(tree).toMatchSnapshot();
Testing component output
This feature enables testing of the component's output. You can inspect the rendered component to verify that it has the expected props, state, or behavior. This is useful for ensuring that your component behaves correctly under various conditions.
import React from 'react';
import renderer from 'react-test-renderer';
const component = renderer.create(<MyComponent prop='value' />);
const instance = component.root;
expect(instance.props.prop).toBe('value');
Interacting with component instances
This feature allows you to interact with the component instances directly. You can simulate events or call methods on the component instance and then re-render. This is useful for testing the component's behavior in response to user interactions or lifecycle events.
import React from 'react';
import renderer from 'react-test-renderer';
class MyComponent extends React.Component {
state = { clicked: false };
handleClick = () => {
this.setState({ clicked: true });
};
render() {
return (<button onClick={this.handleClick}>Click me</button>);
}
}
const component = renderer.create(<MyComponent />);
const button = component.root.findByType('button');
button.props.onClick();
expect(component.toJSON()).toMatchSnapshot();
Other packages similar to react-test-renderer
enzyme
Enzyme is a popular testing utility for React that makes it easier to assert, manipulate, and traverse your React Components' output. Unlike react-test-renderer, Enzyme allows you to simulate events and provides a more jQuery-like API for selecting elements. However, it requires an adapter to work with different versions of React.
react-testing-library
React Testing Library is a set of helpers that let you test React components without relying on their implementation details. This approach encourages better testing practices by focusing on the behavior of components rather than their internal structure. It's more aligned with user interaction compared to react-test-renderer, which is more about rendering components to JSON for snapshot testing.
react-test-renderer
(DEPRECATED)
Deprecation notice
react-test-renderer
is deprecated and no longer maintained. It will be removed in a future version. As of React 19, you will see a console warning when invoking ReactTestRenderer.create()
.
React Testing
This library creates a contrived environment and its APIs encourage introspection on React's internals, which may change without notice causing broken tests. It is instead recommended to use browser-based environments such as jsdom and standard DOM APIs for your assertions.
The React team recommends @testing-library/react
as a modern alternative that uses standard APIs, avoids internals, and promotes best practices.
React Native Testing
The React team recommends @testing-library/react-native as a replacement for react-test-renderer
for native integration tests. This React Native testing-library variant follows the same API design as described above and promotes better testing patterns.
Documentation
This package provides an experimental React renderer that can be used to render React components to pure JavaScript objects, without depending on the DOM or a native mobile environment.
Essentially, this package makes it easy to grab a snapshot of the "DOM tree" rendered by a React DOM or React Native component without using a browser or jsdom.
Documentation: https://reactjs.org/docs/test-renderer.html
Usage:
const ReactTestRenderer = require('react-test-renderer');
const renderer = ReactTestRenderer.create(
<Link page="https://www.facebook.com/">Facebook</Link>
);
console.log(renderer.toJSON());
You can also use Jest's snapshot testing feature to automatically save a copy of the JSON tree to a file and check in your tests that it hasn't changed: https://jestjs.io/blog/2016/07/27/jest-14.html.
19.0.0 (December 5, 2024)
Below is a list of all new features, APIs, deprecations, and breaking changes. Read React 19 release post and React 19 upgrade guide for more information.
Note: To help make the upgrade to React 19 easier, we’ve published a react@18.3 release that is identical to 18.2 but adds warnings for deprecated APIs and other changes that are needed for React 19. We recommend upgrading to React 18.3.1 first to help identify any issues before upgrading to React 19.
New Features
React
- Actions:
startTransition
can now accept async functions. Functions passed to startTransition
are called “Actions”. A given Transition can include one or more Actions which update state in the background and update the UI with one commit. In addition to updating state, Actions can now perform side effects including async requests, and the Action will wait for the work to finish before finishing the Transition. This feature allows Transitions to include side effects like fetch()
in the pending state, and provides support for error handling, and optimistic updates. useActionState
: is a new hook to order Actions inside of a Transition with access to the state of the action, and the pending state. It accepts a reducer that can call Actions, and the initial state used for first render. It also accepts an optional string that is used if the action is passed to a form action
prop to support progressive enhancement in forms.useOptimistic
: is a new hook to update state while a Transition is in progress. It returns the state, and a set function that can be called inside a transition to “optimistically” update the state to expected final value immediately while the Transition completes in the background. When the transition finishes, the state is updated to the new value.use
: is a new API that allows reading resources in render. In React 19, use
accepts a promise or Context. If provided a promise, use
will suspend until a value is resolved. use
can only be used in render but can be called conditionally.ref
as a prop: Refs can now be used as props, removing the need for forwardRef
.- Suspense sibling pre-warming: When a component suspends, React will immediately commit the fallback of the nearest Suspense boundary, without waiting for the entire sibling tree to render. After the fallback commits, React will schedule another render for the suspended siblings to “pre-warm” lazy requests.
React DOM Client
<form> action
prop: Form Actions allow you to manage forms automatically and integrate with useFormStatus
. When a <form> action
succeeds, React will automatically reset the form for uncontrolled components. The form can be reset manually with the new requestFormReset
API.<button> and <input> formAction
prop: Actions can be passed to the formAction
prop to configure form submission behavior. This allows using different Actions depending on the input.useFormStatus
: is a new hook that provides the status of the parent <form> action
, as if the form was a Context provider. The hook returns the values: pending
, data
, method
, and action
.- Support for Document Metadata: We’ve added support for rendering document metadata tags in components natively. React will automatically hoist them into the
<head>
section of the document. - Support for Stylesheets: React 19 will ensure stylesheets are inserted into the
<head>
on the client before revealing the content of a Suspense boundary that depends on that stylesheet. - Support for async scripts: Async scripts can be rendered anywhere in the component tree and React will handle ordering and deduplication.
- Support for preloading resources: React 19 ships with
preinit
, preload
, prefetchDNS
, and preconnect
APIs to optimize initial page loads by moving discovery of additional resources like fonts out of stylesheet loading. They can also be used to prefetch resources used by an anticipated navigation.
React DOM Server
- Added
prerender
and prerenderToNodeStream
APIs for static site generation. They are designed to work with streaming environments like Node.js Streams and Web Streams. Unlike renderToString
, they wait for data to load for HTML generation.
React Server Components
- RSC features such as directives, server components, and server functions are now stable. This means libraries that ship with Server Components can now target React 19 as a peer dependency with a react-server export condition for use in frameworks that support the Full-stack React Architecture. The underlying APIs used to implement a React Server Components bundler or framework do not follow semver and may break between minors in React 19.x. See docs for how to support React Server Components.
Deprecations
- Deprecated:
element.ref
access: React 19 supports ref as a prop, so we’re deprecating element.ref
in favor of element.props.ref
. Accessing will result in a warning. react-test-renderer
: In React 19, react-test-renderer logs a deprecation warning and has switched to concurrent rendering for web usage. We recommend migrating your tests to @testing-library/react or @testing-library/react-native
Breaking Changes
React 19 brings in a number of breaking changes, including the removals of long-deprecated APIs. We recommend first upgrading to 18.3.1
, where we've added additional deprecation warnings. Check out the upgrade guide for more details and guidance on codemodding.
React
- New JSX Transform is now required: We introduced a new JSX transform in 2020 to improve bundle size and use JSX without importing React. In React 19, we’re adding additional improvements like using ref as a prop and JSX speed improvements that require the new transform.
- Errors in render are not re-thrown: Errors that are not caught by an Error Boundary are now reported to window.reportError. Errors that are caught by an Error Boundary are reported to console.error. We’ve introduced
onUncaughtError
and onCaughtError
methods to createRoot
and hydrateRoot
to customize this error handling. - Removed:
propTypes
: Using propTypes
will now be silently ignored. If required, we recommend migrating to TypeScript or another type-checking solution. - Removed:
defaultProps
for functions: ES6 default parameters can be used in place. Class components continue to support defaultProps
since there is no ES6 alternative. - Removed:
contextTypes
and getChildContext
: Legacy Context for class components has been removed in favor of the contextType
API. - Removed: string refs: Any usage of string refs need to be migrated to ref callbacks.
- Removed: Module pattern factories: A rarely used pattern that can be migrated to regular functions.
- Removed:
React.createFactory
: Now that JSX is broadly supported, all createFactory
usage can be migrated to JSX components. - Removed:
react-test-renderer/shallow
: This has been a re-export of react-shallow-renderer since React 18. If needed, you can continue to use the third-party package directly. We recommend using @testing-library/react or @testing-library/react-native instead.
React DOM
- Removed:
react-dom/test-utils
: We’ve moved act
from react-dom/test-utils
to react. All other utilities have been removed. - Removed:
ReactDOM
.render
, ReactDOM
.hydrate
: These have been removed in favor of the concurrent equivalents: ReactDOM
.createRoot
and ReactDOM.hydrateRoot
. - Removed:
unmountComponentAtNode
: Removed in favor of root.unmount()
. - Removed:
ReactDOM
.findDOMNode
: You can replace ReactDOM
.findDOMNode
with DOM Refs.
Notable Changes
React
<Context>
as a provider: You can now render <Context>
as a provider instead of <Context.Provider>
.- Cleanup functions for refs: When the component unmounts, React will call the cleanup function returned from the ref callback.
useDeferredValue
initial value argument: When provided, useDeferredValue
will return the initial value for the initial render of a component, then schedule a re-render in the background with the deferredValue
returned.- Support for Custom Elements: React 19 now passes all tests on Custom Elements Everywhere.
- StrictMode changes:
useMemo
and useCallback
will now reuse the memoized results from the first render, during the second render. Additionally, StrictMode will now double-invoke ref callback functions on initial mount. - UMD builds removed: To load React 19 with a script tag, we recommend using an ESM-based CDN such as esm.sh.
React DOM
- Diffs for hydration errors: In the case of a mismatch, React 19 logs a single error with a diff of the mismatched content.
- Compatibility with third-party scripts and extensions: React will now force a client re-render to fix up any mismatched content caused by elements inserted by third-party JS.
TypeScript Changes
The most common changes can be codemodded with npx types-react-codemod@latest preset-19 ./path-to-your-react-ts-files
.
- Removed deprecated TypeScript types:
ReactChild
(replacement: React.ReactElement | number | string)
ReactFragment
(replacement: Iterable<React.ReactNode>
)ReactNodeArray
(replacement: ReadonlyArray<React.ReactNode>
)ReactText
(replacement: number | string
)VoidFunctionComponent
(replacement: FunctionComponent
)VFC
(replacement: FC
)- Moved to
prop-types
: Requireable
, ValidationMap
, Validator
, WeakValidationMap
- Moved to
create-react-class
: ClassicComponentClass
, ClassicComponent
, ClassicElement
, ComponentSpec
, Mixin
, ReactChildren
, ReactHTML
, ReactSVG
, SFCFactory
- Disallow implicit return in refs: refs can now accept cleanup functions. When you return something else, we can’t tell if you intentionally returned something not meant to clean up or returned the wrong value. Implicit returns of anything but functions will now error.
- Require initial argument to
useRef
: The initial argument is now required to match useState
, createContext
etc - Refs are mutable by default: Ref objects returned from
useRef()
are now always mutable instead of sometimes being immutable. This feature was too confusing for users and conflicted with legit cases where refs were managed by React and manually written to. - Strict
ReactElement
typing: The props of React elements now default to unknown
instead of any
if the element is typed as ReactElement
- JSX namespace in TypeScript: The global
JSX
namespace is removed to improve interoperability with other libraries using JSX. Instead, the JSX namespace is available from the React package: import { JSX } from 'react'
- Better
useReducer
typings: Most useReducer
usage should not require explicit type arguments.
For example,
-useReducer<React.Reducer<State, Action>>(reducer)
+useReducer(reducer)
or
-useReducer<React.Reducer<State, Action>>(reducer)
+useReducer<State, Action>(reducer)
All Changes
React
- Add support for async Actions (#26621, #26726, #28078, #28097, #29226, #29618, #29670, #26716 by @acdlite and @sebmarkbage)
- Add
useActionState()
hook to update state based on the result of a Form Action (#27270, #27278, #27309, #27302, #27307, #27366, #27370, #27321, #27374, #27372, #27397, #27399, #27460, #28557, #27570, #27571, #28631, #28788, #29694, #29695, #29694, #29665, #28232, #28319 by @acdlite, @eps1lon, and @rickhanlonii) - Add
use()
API to read resources in render (#25084, #25202, #25207, #25214, #25226, #25247, #25539, #25538, #25537, #25543, #25561, #25620, #25615, #25922, #25641, #25634, #26232, #26536, #26739, #28233 by @acdlite, @MofeiZ, @sebmarkbage, @sophiebits, @eps1lon, and @hansottowirtz) - Add
useOptimistic()
hook to display mutated state optimistically during an async mutation (#26740, #26772, #27277, #27453, #27454, #27936 by @acdlite) - Added an
initialValue
argument to useDeferredValue()
hook (#27500, #27509, #27512, #27888, #27550 by @acdlite) - Support refs as props, warn on
element.ref
access (#28348, #28464, #28731 by @acdlite) - Support Custom Elements (#22184, #26524, #26523, #27511, #24541 by @josepharhar, @sebmarkbage, @gnoff and @eps1lon)
- Add ref cleanup function (#25686, #28883, #28910 by @sammy-SC, @jackpope, and @kassens)
- Sibling pre-rendering replaced by sibling pre-warming (#26380, #26549, #30761, #30800, #30762, #30879, #30934, #30952, #31056, #31452 by @sammy-SC, @acdlite, @gnoff, @jackpope, @rickhanlonii)
- Don’t rethrow errors at the root (#28627, #28641 by @sebmarkbage)
- Batch sync discrete, continuous, and default lanes (#25700 by @tyao1)
- Switch
<Context>
to mean <Context.Provider>
(#28226 by @gaearon) - Changes to StrictMode
- Add support for rendering BigInt (#24580 by @eps1lon)
act()
no longer checks shouldYield
which can be inaccurate in test environments (#26317 by @acdlite)- Warn when keys are spread with props (#25697, #26080 by @sebmarkbage and @kassens)
- Generate sourcemaps for production build artifacts (#26446 by @markerikson)
- Improve stack diffing algorithm (#27132 by @KarimP)
- Suspense throttling lowered from 500ms to 300ms (#26803 by @acdlite)
- Lazily propagate context changes (#20890 by @acdlite and @gnoff)
- Immediately rerender pinged fiber (#25074 by @acdlite)
- Move update scheduling to microtask (#26512 by @acdlite)
- Consistently apply throttled retries (#26611, #26802 by @acdlite)
- Suspend Thenable/Lazy if it's used in React.Children (#28284 by @sebmarkbage)
- Detect infinite update loops caused by render phase updates (#26625 by @acdlite)
- Update conditional hooks warning (#29626 by @sophiebits)
- Update error URLs to go to new docs (#27240 by @rickhanlonii)
- Rename the
react.element
symbol to react.transitional.element
(#28813 by @sebmarkbage) - Fix crash when suspending in shell during
useSyncExternalStore()
re-render (#27199 by @acdlite) - Fix incorrect “detected multiple renderers" error in tests (#22797 by @eps1lon)
- Fix bug where effect cleanup may be called twice after bailout (#26561 by @acdlite)
- Fix suspending in shell during discrete update (#25495 by @acdlite)
- Fix memory leak after repeated setState bailouts (#25309 by @acdlite)
- Fix
useSyncExternalStore()
dropped update when state is dispatched in render phase (#25578 by @pandaiolo) - Fix logging when rendering a lazy fragment (#30372 by @tom-sherman)
- Remove string refs (#25383, #28322 by @eps1lon and @acdlite)
- Remove Legacy Context (#30319 by @kassens)
- Remove
RefreshRuntime.findAffectedHostInstances
(#30538 by @gaearon) - Remove client caching from
cache()
API (#27977, #28250 by @acdlite and @gnoff) - Remove
propTypes
(#28324, #28326 by @gaearon) - Remove
defaultProps
support, except for classes (#28733 by @acdlite) - Remove UMD builds (#28735 by @gnoff)
- Remove delay for non-transition updates (#26597 by @acdlite)
- Remove
createFactory
(#27798 by @kassens)
React DOM
- Adds Form Actions to handle form submission (#26379, #26674, #26689, #26708, #26714, #26735, #26846, #27358, #28056 by @sebmarkbage, @acdlite, and @jupapios)
- Add
useFormStatus()
hook to provide status information of the last form submission (#26719, #26722, #26788, #29019, #28728, #28413 by @acdlite and @eps1lon) - Support for Document Metadata. Adds
preinit
, preinitModule
, preconnect
, prefetchDNS
, preload
, and preloadModule
APIs.
- #25060, #25243, #25388, #25432, #25436, #25426, #25500, #25480, #25508, #25515, #25514, #25532, #25536, #25534, #25546, #25559, #25569, #25599, #25689, #26106, #26152, #26239, #26237, #26280, #26154, #26256, #26353, #26427, #26450, #26502, #26514, #26531, #26532, #26557, #26871, #26881, #26877, #26873, #26880, #26942, #26938, #26940, #26939, #27030, #27201, #27212, #27217, #27218, #27220, #27224, #27223, #27269, #27260, #27347, #27346, #27361, #27400, #27541, #27610, #28110, #29693, #29732, #29811, #27586, #28069 by @gnoff, @sebmarkbage, @acdlite, @kassens, @sokra, @sweetliquid
- Add
fetchPriority
to <img>
and <link>
(#25927 by @styfle) - Add support for SVG
transformOrigin
prop (#26130 by @arav-ind) - Add support for
onScrollEnd
event (#26789 by @devongovett) - Allow
<hr>
as child of <select>
(#27632 by @SouSingh) - Add support for Popover API (#27981 by @eps1lon)
- Add support for
inert
(#24730 by @eps1lon) - Add support for
imageSizes
and imageSrcSet
(#22550 by @eps1lon) - Synchronously flush transitions in popstate events (#26025, #27559, #27505, #30759 by @tyao1 and @acdlite)
flushSync
exhausts queue even if something throws (#26366 by @acdlite)- Throw error if
react
and react-dom
versions don’t match (#29236 by @acdlite) - Ensure
srcset
and src
are assigned last on <img>
instances (#30340 by @gnoff) - Javascript URLs are replaced with functions that throw errors (#26507, #29808 by @sebmarkbage and @kassens)
- Treat toggle and beforetoggle as discrete events (#29176 by @eps1lon)
- Filter out empty
src
and href
attributes (unless for <a href=”” />
) (#18513, #28124 by @bvaughn and @eps1lon) - Fix unitless
scale
style property (#25601 by @JonnyBurger) - Fix
onChange
error message for controlled <select>
(#27740 by @Biki-das) - Fix focus restore in child windows after element reorder (#30951 by @ling1726)
- Remove
render
, hydrate
, findDOMNode
, unmountComponentAtNode
, unstable_createEventHandle
, unstable_renderSubtreeIntoContainer
, and unstable_runWithPriority
. Move createRoot
and hydrateRoot
to react-dom/client
. (#28271 by @gnoff) - Remove
test-utils
(#28541 by @eps1lon) - Remove
unstable_flushControlled
(#26397 by @kassens) - Remove legacy mode (#28468 by @gnoff)
- Remove
renderToStaticNodeStream()
(#28873 by @gnoff) - Remove
unstable_renderSubtreeIntoContainer
(#29771 by @kassens)
React DOM Server
- Stable release of React Server Components (Many, many PRs by @sebmarkbage, @acdlite, @gnoff, @sammy-SC, @gaearon, @sophiebits, @unstubbable, @lubieowoce)
- Support Server Actions (#26124, #26632, #27459 by @sebmarkbage and @acdlite)
- Changes to SSR
- Add external runtime which bootstraps hydration on the client for binary transparency (#25437, #26169, #25499 by @MofeiZ and @acdlite)
- Support subresource integrity for
bootstrapScripts
and bootstrapModules
(#25104 by @gnoff) - Fix null bytes written at text chunk boundaries (#26228 by @sophiebits)
- Fix logic around attribute serialization (#26526 by @gnoff)
- Fix precomputed chunk cleared on Node 18 (#25645 by @feedthejim)
- Optimize end tag chunks (#27522 by @yujunjung)
- Gracefully handle suspending in DOM configs (#26768 by @sebmarkbage)
- Check for nullish values on ReactCustomFormAction (#26770 by @sebmarkbage)
- Preload
bootstrapModules
, bootstrapScripts
, and update priority queue (#26754, #26753, #27190, #27189 by @gnoff) - Client render the nearest child or parent suspense boundary if replay errors or is aborted (#27386 by @sebmarkbage)
- Don't bail out of flushing if we still have pending root tasks (#27385 by @sebmarkbage)
- Ensure Resumable State is Serializable (#27388 by @sebmarkbage)
- Remove extra render pass when reverting to client render (#26445 by @acdlite)
- Fix unwinding context during selective hydration (#25876 by @tyao1)
- Stop flowing and then abort if a stream is cancelled (#27405 by @sebmarkbage)
- Pass cancellation reason to abort (#27536 by @sebmarkbage)
- Add
onHeaders
entrypoint option (#27641, #27712 by @gnoff) - Escape
<style>
and <script>
textContent to enable rendering inner content without dangerouslySetInnerHTML (#28870, #28871 by @gnoff) - Fallback to client replaying actions for Blob serialization (#28987 by @sebmarkbage)
- Render Suspense fallback if boundary contains new stylesheet during sync update (#28965 by @gnoff)
- Fix header length tracking (#30327 by @gnoff)
- Use
srcset
to trigger load event on mount (#30351 by @gnoff) - Don't perform work when closing stream (#30497 by @gnoff)
- Allow aborting during render (#30488, #30730 by @gnoff)
- Start initial work immediately (#31079 by @gnoff)
- A transition flowing into a dehydrated boundary no longer suspends when showing fallback (#27230 by @acdlite)
- Fix selective hydration triggers false update loop error (#27439 by @acdlite)
- Warn for Child Iterator of all types but allow Generator Components (#28853 by @sebmarkbage)
- Include regular stack trace in serialized errors (#28684, #28738 by @sebmarkbage)
- Aborting early no longer infinitely suspends (#24751 by @sebmarkbage)
- Fix hydration warning suppression in text comparisons (#24784 by @gnoff)
- Changes to error handling in SSR
- Add Bun streaming server renderer (#25597 by @colinhacks)
- Add nonce support to bootstrap scripts (#26738 by @danieltott)
- Add
crossorigin
support to bootstrap scripts (#26844 by @HenriqueLimas) - Support
nonce
and fetchpriority
in preload links (#26826 by @liuyenwei) - Add
referrerPolicy
to ReactDOM.preload()
(#27096 by @styfle) - Add server condition for
react/jsx-dev-runtime
(#28921 by @himself65) - Export version (#29596 by @unstubbable)
- Rename the secret export of Client and Server internals (#28786, #28789 by @sebmarkbage)
- Remove layout effect warning on server (#26395 by @rickhanlonii)
- Remove
errorInfo.digest
from onRecoverableError
(#28222 by @gnoff)
ReactTestRenderer
React Reconciler
React-Is
useSyncExternalStore