mention the payload limit of 64 KiB for sendBeacon()

[codersjj]

Description

Mention the payload limit of 64 KiB for sendBeacon().

Motivation

Additional details

• Fetch specification reference: HTTP-network-or-cache fetch defines the 64 KiB limit for keepalive requests
• Firefox bug 2008613

Related issues and pull requests

Fixes #42932

Relates to mdn/browser-compat-data#20721, #42957

[github-actions]

Preview URLs (1 page)

• /en-US/docs/Web/API/Navigator/sendBeacon

(comment last updated: 2026-01-30 02:51:02)

[wbamberg]

The limitation should be added to the documentation for the data parameter, not here, and does not need to link to the Fetch spec: it should just be described as a limitation of this API.

[codersjj]

The limitation should be added to the documentation for the data parameter, not here, and does not need to link to the Fetch spec: it should just be described as a limitation of this API.

That makes sense, the 64 KiB limit belongs under the data parameter rather than the return value. I'll move it there with a clear, concise note.