💥 ResizeObserver Error in React

(Why it appears only in DEV and scares everyone 😱)

" Uncaught runtime errors:
ResizeObserver loop completed with undelivered notifications " 

If you have ever seen this red screen suddenly appear while scrolling, resizing, or editing an AG Grid…

👉 Welcome to the ResizeObserver Club 🎉

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🤔 What is ResizeObserver?

ResizeObserver is a browser API that watches:

• Element width changes
• Element height changes
• Layout recalculations

Modern UI libraries like:

• AG Grid
• Material UI
• Ant Design

use ResizeObserver heavily to keep layouts perfect.

AG Grid uses it a LOT 👀

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😈 What does this error actually mean?

In simple words:

"Hey browser, I tried to recalculate layout again and again…
but UI kept changing continuously 😤"

So the browser says:

"Enough! I’m stopping this infinite resize loop." 💥

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🧠 Real Reasons Why This Happens (AG Grid Edition)

1️⃣ Dynamic height inside CellRenderer

Example:

Height keeps changing → ResizeObserver keeps firing 🔁

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2️⃣ autoHeight + long wrapping text

When you combine:

• autoHeight
• white-space: normal
• long text

AG Grid tries to measure height repeatedly.

Result: 💥 ResizeObserver error

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3️⃣ Missing getRowId (VERY COMMON)

Without this:

getRowId={(params) => params.data.id}

AG Grid thinks:

"One cell changed? Let me re-render EVERYTHING" 😈

ResizeObserver gets overwhelmed.

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4️⃣ Custom dropdowns floating outside grid

When dropdowns are:

• position: absolute
• Rendered outside grid DOM

Scrolling + resize = chaos 🔥

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🤯 Why this happens ONLY in DEV?

This is the most confusing part.

✅ Reason 1: React StrictMode

In DEV mode:

• Components render twice
• Effects run twice

React does this intentionally to catch bugs.

Production build:

👉 Clean
👉 Single render
👉 No red screen

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✅ Reason 2: DEV shows runtime overlay

DEV environment shows:

• Warnings as full-screen errors
• ResizeObserver warnings aggressively

Production:

👉 Console warning only
👉 UI continues working

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✅ Reason 3: Slower DEV rendering

DEV mode is slower.

Slow rendering + heavy DOM = resize timing issues

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🛠️ Correct Ways to Fix (Production Safe)

✔ Fix 1: Always define getRowId

<AgGridReact
  getRowId={(params) => params.data.id}
/>

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✔ Fix 2: Avoid dynamic height changes

// ✅ Better
<div style={{ minHeight: 32 }}>
  <Dropdown hidden={!checked} />
</div>

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✔ Fix 3: Use AG Grid built-in editors

Instead of custom dropdowns:

cellEditor: 'agSelectCellEditor'

AG Grid handles:

• Scroll
• Resize
• Close on blur

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✔ Fix 4: Suppress ResizeObserver safely

<AgGridReact
  suppressBrowserResizeObserver={true}
  stopEditingWhenCellsLoseFocus={true}
/>

✔ Officially supported

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😂 Developer Joke (True Story)

"It works in production, so ignore DEV error"
— Famous words before next sprint 😄

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🧠 Golden Rules to Avoid This Forever

• ✔ Stable row IDs
• ✔ Avoid height-changing DOM
• ✔ Prefer AG Grid editors
• ✔ Avoid re-setting full rowData

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🏁 Wrapping Up

ResizeObserver error is not a bug — it’s a signal.

It tells you:

• Your UI is doing too much resizing
• Your grid needs stability

Fix the cause, not the warning.

💬 If you faced this issue and fixed it differently, share your experience — someone else is debugging this right now 😄