f247ebaf44
## Summary Follow-up to https://github.com/vercel/next.js/pull/89823 with the actual changes to React. Replaces the `JSON.parse` reviver callback in `initializeModelChunk` with a two-step approach: plain `JSON.parse()` followed by a recursive `reviveModel()` post-process (same as in Flight Reply Server). This yields a **~75% speedup** in RSC chunk deserialization. | Payload | Original (ms) | Walk (ms) | Speedup | |---------|---------------|-----------|---------| | Small (2 elements, 142B) | 0.0024 | 0.0007 | **+72%** | | Medium (~12 elements, 914B) | 0.0116 | 0.0031 | **+73%** | | Large (~90 elements, 16.7KB) | 0.1836 | 0.0451 | **+75%** | | XL (~200 elements, 25.7KB) | 0.3742 | 0.0913 | **+76%** | | Table (1000 rows, 110KB) | 3.0862 | 0.6887 | **+78%** | ## Problem `createFromJSONCallback` returns a reviver function passed as the second argument to `JSON.parse()`. This reviver is called for **every key-value pair** in the parsed JSON. While the logic inside the reviver is lightweight, the dominant cost is the **C++ → JavaScript boundary crossing** — V8's `JSON.parse` is implemented in C++, and calling back into JavaScript for every node incurs significant overhead. Even a trivial no-op reviver `(k, v) => v` makes `JSON.parse` **~4x slower** than bare `JSON.parse` without a reviver: ``` 108 KB payload: Bare JSON.parse: 0.60 ms Trivial reviver: 2.95 ms (+391%) ``` ## Change Replace the reviver with a two-step process: 1. `JSON.parse(resolvedModel)` — parse the entire payload in C++ with no callbacks 2. `reviveModel` — recursively walk the resulting object in pure JavaScript to apply RSC transformations The `reviveModel` function includes additional optimizations over the original reviver: - **Short-circuits plain strings**: only calls `parseModelString` when the string starts with `$`, skipping the vast majority of strings (class names, text content, etc.) - **Stays entirely in JavaScript** — no C++ boundary crossings during the walk ## Results You can find the related applications in the [Next.js PR ](https://github.com/vercel/next.js/pull/89823)as I've been testing this on Next.js applications. ### Table as Server Component with 1000 items Before: ``` "min": 13.782875000000786, "max": 22.23400000000038, "avg": 17.116868530000083, "p50": 17.10766700000022, "p75": 18.50787499999933, "p95": 20.426249999998618, "p99": 21.814125000000786 ``` After: ``` "min": 10.963916999999128, "max": 18.096083000000363, "avg": 13.543286884999988, "p50": 13.58350000000064, "p75": 14.871791999999914, "p95": 16.08429099999921, "p99": 17.591458000000785 ``` ### Table as Client Component with 1000 items Before: ``` "min": 3.888875000000553, "max": 9.044959000000745, "avg": 4.651271475000067, "p50": 4.555749999999534, "p75": 4.966624999999112, "p95": 5.47754200000054, "p99": 6.109499999998661 ```` After: ``` "min": 3.5986250000005384, "max": 5.374291000000085, "avg": 4.142990245000046, "p50": 4.10570799999914, "p75": 4.392041999999492, "p95": 4.740084000000934, "p99": 5.1652500000000146 ``` ### Nested Suspense Before: ``` Requests: 200 Min: 73ms Max: 106ms Avg: 78ms P50: 77ms P75: 80ms P95: 85ms P99: 94ms ``` After: ``` Requests: 200 Min: 56ms Max: 67ms Avg: 59ms P50: 58ms P75: 60ms P95: 65ms P99: 66ms ``` ### Even more nested Suspense (double-level Suspense) Before: ``` Requests: 200 Min: 159ms Max: 208ms Avg: 169ms P50: 167ms P75: 173ms P95: 183ms P99: 188ms ``` After: ``` Requests: 200 Min: 125ms Max: 170ms Avg: 134ms P50: 132ms P75: 138ms P95: 148ms P99: 160ms ``` ## How did you test this change? Ran it across many Next.js benchmark applications. The entire Next.js test suite passes with this change. --------- Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>
react-client
This is an experimental package for consuming custom React streaming models.
Its API is not as stable as that of React, React Native, or React DOM, and does not follow the common versioning scheme.
Use it at your own risk.