Cannot perform %TypedArray%.prototype.fill on a detached ArrayBuffer

[opeologist]

Is this a support request?

No

Describe the bug

After updating our application to the latest version of next (v15.5.2) from our previous (v.15.4.2), we're experiencing random crashes to our dev server after saving a few times intermittently. Our app follows the guidance in the documentation for setting up launchdarkly appropriately and has been working without issue up until we updated next to its latest.

To reproduce

scaffold a create-next-app app, install @launchdarkly/node-server-sdk, implement and use the LD client to fetch some flags in a server component, and make miscellaneous changes to the app by saving/hot-reloading the app...? I'm not sure how it's occurring or how to replicate consistently, just that this environment creates the issue eventually

Expected behavior

the crash should not occur

Logs

2025-08-20T20:56:43 error uncaughtException: Cannot perform %TypedArray%.prototype.fill on a detached ArrayBuffer
[next] TypeError: Cannot perform %TypedArray%.prototype.fill on a detached ArrayBuffer
[next]     at Uint32Array.fill (<anonymous>)
[next]     at LruCache.clear (webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-server-sdk-common/dist/cache/LruCache.js:76:20)
[next]     at ContextDeduplicator.flush (webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-server-sdk-common/dist/events/ContextDeduplicator.js:17:32)
[next]     at Timeout.eval [as _onTimeout] (webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-sdk-common/dist/cjs/index.cjs:2002:44)
[next]     at listOnTimeout (node:internal/timers:588:17)
[next]     at process.processTimers (node:internal/timers:523:7) {"error":{},"stack":"TypeError: Cannot perform %TypedArray%.prototype.fill on a detached ArrayBuffer\n    at Uint32Array.fill (<anonymous>)\n    at LruCache.clear (webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-server-sdk-common/dist/cache/LruCache.js:76:20)\n    at ContextDeduplicator.flush (webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-server-sdk-common/dist/events/ContextDeduplicator.js:17:32)\n    at Timeout.eval [as _onTimeout] (webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-sdk-common/dist/cjs/index.cjs:2002:44)\n    at listOnTimeout (node:internal/timers:588:17)\n    at process.processTimers (node:internal/timers:523:7)","exception":true,"date":"Wed Aug 20 2025 15:56:43 GMT-0500 (Central Daylight Time)","process":{"pid":19189,"uid":502,"gid":20,"cwd":"/Users/internal","execPath":"/Users/internal/Library/Application Support/fnm/node-versions/v22.17.1/installation/bin/node","version":"v22.17.1","argv":["/Users/internal/Library/Application Support/fnm/node-versions/v22.17.1/installation/bin/node","/Users/internal/node_modules/next/dist/server/lib/start-server.js"],"memoryUsage":{"rss":1473118208,"heapTotal":622657536,"heapUsed":554944816,"external":641127109,"arrayBuffers":616006113}},"os":{"loadavg":[30.505859375,24.3154296875,18.9453125],"uptime":179130},"trace":[{"column":null,"file":null,"function":"Uint32Array.fill","line":null,"method":"fill","native":false},{"column":20,"file":"webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-server-sdk-common/dist/cache/LruCache.js","function":"LruCache.clear","line":76,"method":"clear","native":false},{"column":32,"file":"webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-server-sdk-common/dist/events/ContextDeduplicator.js","function":"ContextDeduplicator.flush","line":17,"method":"flush","native":false},{"column":44,"file":"webpack-internal:///(rsc)/./node_modules/@launchdarkly/js-sdk-common/dist/cjs/index.cjs","function":"Timeout.eval [as _onTimeout]","line":2002,"method":"eval [as _onTimeout]","native":false},{"column":17,"file":"node:internal/timers","function":"listOnTimeout","line":588,"method":null,"native":false},{"column":7,"file":"node:internal/timers","function":"process.processTimers","line":523,"method":"processTimers","native":false}]}

SDK version

"@launchdarkly/node-server-sdk": "^9.7.6"

Language version, developer tools

Node.js, next dev server

OS/platform

macOS 15.6.1

[opeologist]

is there anyone that can provide an update on this? would appreciate any information related. thank you!

[kinyoklion]

Hey @opeologist,

Sorry for the delay. The SDK creates the buffer and then never takes any action that detaches it. It just access elements and then fills it. It sounds like an issue with the hot reload mechanism potentially? That some code is still executing while partially through the hot reload.

The SDK itself though doesn't have any insight into the hot load process. It seems like something that should be fixed against next.

Theoretically we could check if the array buffers are detached, but being as we don't detach them, or provide any way to detach them, it seems like a very problematic addition. This situation in a non-development environment would represent a serious problem with integrity.

Thank you,
Ryan

[opeologist]

thanks @kinyoklion for the update! i'll see about investigating from the next side to see if there's some change they've made that would impact this. the weird thing is that it will happen even if you don't hot-reload after some seemingly predetermined interval, so maybe it's something to do with the dev server socket connection.. anyways, i'll close this, thank you!

[joaom182]

Same issue here, and it is very annoying, the application logs are flooded with these errors. I think LD team need to take a look at it ASAP.