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Regression: Next/Dynamic Conditionally Importing Client Components Adds Both To Client Bundle In Next.Js 15

Next.js 15 preloads all dynamic imports inside client components, causing both conditional chunks to be sent to the client, increasing initial JavaScript size and TBT compared to Next.js 14. The issue requires a user-land workaround until an upstream fix is released.

highConfidence 75%Next.js Affected V15.3.3

Origin Analysis

Introduced in Next.js 15, likely by PR #65486, the client-side preload logic for next/dynamic now eagerly preloads all dynamic chunks referenced by a client component, even when they are conditionally rendered. In Next.js 14, only the chunk for the actually rendered component was requested.

Create a Next.js 15.3.3 app with two client components ClientA and ClientB. Use next/dynamic to import them conditionally inside a client component. Render only one based on state. Build and analyze the client bundle: both chunks are included initially, whereas Next.js 14 only includes the rendered chunk.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

This workaround disables server-side rendering for the dynamic components. If the components rely on SSR for SEO or initial content, they will show a fallback on the server and may cause layout shift. Also ensure all imports are client components ('use client') to avoid server/client mismatch. Rollback: once Next.js provides an official fix, replace React.lazy with next/dynamic to restore SSR. Test with ssr:false first in a staging environment before deploying, and monitor for hydration errors.