Bug: Large TypedArray props hang browser in dev mode in 19.2.X

[jschlechtvjt]

Passing a large TypedArray, e.g. Float32Array(25000000), as a prop to a component, causes rendering to hang in development mode in React >= 19.2. Production mode is unaffected. Earlier versions of React (<= 19.1.5) are unaffected in both dev and prod modes.

Potentially related to #35126.

React version: >=19.2

Steps To Reproduce

Render the component React192TypedArrayPropIssue in the following code example:

import React from 'react';

function SlowToRenderInDevMode({array}: {array: Uint8Array}) {
  return (
    <>
      <div>{array.length}</div>
      <button>unclickable</button>    
    </>
  );
}

export function React192TypedArrayPropIssue() {
  // const [array, setArray] = React.useState<Float32Array>(new Float32Array());
  const [array, setArray] = React.useState<Uint8Array>(new Uint8Array());

  React.useEffect(() => {
    setArray(new Uint8Array(5000 * 5000));
  }, []);

  return (
    <SlowToRenderInDevMode array={array}/>
  )
}

The current behavior

For a Uint8Array or Float32Array of length of 25000000, the render takes > 10seconds and freezes the browser.
Non-typed arrays are unaffected by the issue.

The expected behavior

In production mode (or earlier versions of React <=19.1.5) render is immediate.

[brandonedwards12314-collab]

Thanks for the report — this is interesting, especially since it only affects dev mode starting in 19.2 and doesn’t reproduce in production.

…

On Thu, Apr 2, 2026, 4:05 PM jschlechtvjt ***@***.***> wrote: *jschlechtvjt* created an issue (facebook/react#36200) <#36200> Passing a large TypedArray, e.g. Float32Array(25000000), as a prop to a component, causes rendering to hang in development mode in React >= 19.2. Production mode is unaffected. Earlier versions of React (<= 19.1.5) are unaffected in both dev and prod modes. Potentially related to #35126 <#35126>. React version: >=19.2 Steps To Reproduce Render the component React192TypedArrayPropIssue in the following code example: import React from 'react'; function SlowToRenderInDevMode({array}: {array: Uint8Array}) { return ( <> <div>{array.length}</div> <button>unclickable</button> </> );} export function React192TypedArrayPropIssue() { // const [array, setArray] = React.useState<Float32Array>(new Float32Array()); const [array, setArray] = React.useState<Uint8Array>(new Uint8Array()); React.useEffect(() => { setArray(new Uint8Array(5000 * 5000)); }, []); return ( <SlowToRenderInDevMode array={array}/> )} The current behavior For a Uint8Array or Float32Array of length of 25000000, the render takes > 10seconds and freezes the browser. Non-typed arrays are unaffected by the issue. The expected behavior In production mode (or earlier versions of React <=19.1.5) render is immediate. — Reply to this email directly, view it on GitHub <#36200?email_source=notifications&email_token=B7BTL4FTDM2ZZTSPOHHUAZD4T3IX5A5CNFSL4Z3JMQ5C6L3HNF2C22DVMIXUS43TOVSS6NBRHE3DSOBRHE4DPJTSMVQXG33OVJZXKYTTMNZGSYTFMSSWK5TFNZ2KYZTPN52GK4S7MNWGSY3L>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/B7BTL4ES56WXHPZJ7KXX3UL4T3IX5AVCNFSM6AAAAACXLBYRTCVHI2DSMVQWIX3LMV43ASLTON2WKOZUGE4TMOJYGE4TQNY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[lotfimaria331-ops]

We can confirm there seems to be a regression in development mode starting from React 19.2 when handling large TypedArrays as props. The fact that production mode and earlier versions (≤19.1.5) are unaffected is especially useful in narrowing this down. Le jeu. 2 avr. 2026, 16:05, jschlechtvjt ***@***.***> a écrit :

…

*jschlechtvjt* created an issue (facebook/react#36200) <#36200> Passing a large TypedArray, e.g. Float32Array(25000000), as a prop to a component, causes rendering to hang in development mode in React >= 19.2. Production mode is unaffected. Earlier versions of React (<= 19.1.5) are unaffected in both dev and prod modes. Potentially related to #35126 <#35126>. React version: >=19.2 Steps To Reproduce Render the component React192TypedArrayPropIssue in the following code example: import React from 'react'; function SlowToRenderInDevMode({array}: {array: Uint8Array}) { return ( <> <div>{array.length}</div> <button>unclickable</button> </> );} export function React192TypedArrayPropIssue() { // const [array, setArray] = React.useState<Float32Array>(new Float32Array()); const [array, setArray] = React.useState<Uint8Array>(new Uint8Array()); React.useEffect(() => { setArray(new Uint8Array(5000 * 5000)); }, []); return ( <SlowToRenderInDevMode array={array}/> )} The current behavior For a Uint8Array or Float32Array of length of 25000000, the render takes > 10seconds and freezes the browser. Non-typed arrays are unaffected by the issue. The expected behavior In production mode (or earlier versions of React <=19.1.5) render is immediate. — Reply to this email directly, view it on GitHub <#36200?email_source=notifications&email_token=B7VCPZVF4XFSP3FQP54M7O34T3IX7A5CNFSL4Z3JMQ5C6L3HNF2C22DVMIXUS43TOVSS6NBRHE3DSOBRHE4DPJTSMVQXG33OVJZXKYTTMNZGSYTFMSSWK5TFNZ2KYZTPN52GK4S7MNWGSY3L>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/B7VCPZWJYBPDW24X7AHFOAT4T3IX7AVCNFSM6AAAAACXLBYRTCVHI2DSMVQWIX3LMV43ASLTON2WKOZUGE4TMOJYGE4TQNY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>