ResizeObserver loop completed with undelivered notifications.

Browser · updated 2026-11-13

Chrome reports this to window.onerror when a ResizeObserver callback resizes an observed element and the browser has to skip notifications to avoid an endless loop in that frame. There is no stack trace (the error object is null and the file is the page), so trackers group every occurrence together. It often comes from a library (editors, auto-sizing textareas, charts), not your own code.

Uncaught error event:
  message:  ResizeObserver loop completed with undelivered notifications.
  filename: https://shop.example/checkout
  lineno:   0
  error:    null

Quick fix

If it is your observer: don't change the observed element's size synchronously in the callback. Defer the change to requestAnimationFrame and only apply it when the value differs. In headless Chrome, growing the element in the callback raised the error every frame (41 times in 0.6 s); setting it once still raised it once; the same change inside requestAnimationFrame with a guard raised it 0 times. If it comes from a library and nothing looks broken, upgrade the library, then ignore the error group.

1. Search your code for new ResizeObserver: a callback that sets width, height, padding or content on the element it observes is the cause.
2. Move that change into requestAnimationFrame, and compare with the current value before setting it.
3. No observer of yours? Check which components mount on the page (rich text editors, auto-resizing textareas, chart libraries) and upgrade them.
4. If nothing on the page misbehaves, ignore the error group (runheed_ignore_error, or ignoreErrors in Sentry.init) so it stops counting against real errors.

const ro = new ResizeObserver(([entry]) => {
  const target = Math.ceil(entry.contentRect.width / 8) * 8;
  requestAnimationFrame(() => {
    if (panel.offsetWidth !== target) panel.style.width = target + 'px';
  });
});
ro.observe(panel);

// Library you can't change, and nothing breaks: drop it at the SDK
Sentry.init({ dsn, ignoreErrors: [/^ResizeObserver loop/] });

Read https://runheed.com/errors/resizeobserver-loop-completed-with-undelivered-notifications.md and fix this error in this project.

Why it happens

Other fixes

• Use CSS (flex, grid, aspect-ratio, container queries) for layouts that only need to follow their container, with no observer at all.
• Debounce observers that do expensive work, so one resize burst causes one layout pass.

Same error, other wording

• ResizeObserver loop limit exceeded
• Uncaught Error: ResizeObserver loop completed with undelivered notifications.

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References: W3C Resize Observer specification: error reporting, MDN: ResizeObserver

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