TURBOPACK: downgrade insert js code by fireairforce · Pull Request #123 · utooland/next.js

fireairforce · 2026-03-17T18:17:19Z

downgrade insert js code to avoid low devices.

gemini-code-assist · 2026-03-17T18:17:52Z

Summary of Changes

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This pull request significantly enhances the compatibility of Turbopack's generated JavaScript code by downgrading certain modern syntax features and implementing a more resilient global object detection mechanism. The primary goal is to ensure that applications built with Turbopack function correctly across a wider array of client environments, including older or less capable devices, by avoiding reliance on newer JavaScript features.

Highlights

Global Object Fallback: Implemented a robust fallback mechanism for accessing the global object (e.g., globalThis, self, window, global) to ensure compatibility across diverse JavaScript environments, especially older ones that may not support globalThis.
JavaScript Syntax Downgrade: Replaced modern JavaScript syntax (e.g., const, arrow functions) with older, more widely supported equivalents (var, traditional function declarations) in generated runtime code to enhance compatibility.
Improved Device Compatibility: These changes collectively aim to prevent issues on 'low devices' by ensuring the generated JavaScript code is compatible with a broader range of JavaScript engines and environments.

Changelog

turbopack/crates/turbopack-browser/src/chunking_context.rs
- Added a constant GLOBAL_THIS_FALLBACK_EXPR for robust global object detection.
turbopack/crates/turbopack-browser/src/ecmascript/content.rs
- Imported GLOBAL_THIS_FALLBACK_EXPR for global object access.
- Updated chunk loading code to utilize the new global object fallback expression.
turbopack/crates/turbopack-browser/src/ecmascript/evaluate/chunk.rs
- Imported GLOBAL_THIS_FALLBACK_EXPR for global object access.
- Updated chunk evaluation code to utilize the new global object fallback expression.
turbopack/crates/turbopack-browser/src/ecmascript/list/content.rs
- Imported GLOBAL_THIS_FALLBACK_EXPR for global object access.
- Updated chunk list loading code to utilize the new global object fallback expression.
turbopack/crates/turbopack-ecmascript-runtime/src/browser_runtime.rs
- Defined GLOBAL_THIS_FALLBACK_EXPR locally within the file.
- Introduced a __turbopack_global__ variable to encapsulate global object access using the fallback.
- Downgraded JavaScript variable declarations from const to var in generated runtime code.
- Updated references to globalThis to use __turbopack_global__ for chunk loading and asset suffix logic.
turbopack/crates/turbopack-ecmascript/src/async_chunk/module.rs
- Converted arrow functions to traditional function expressions in async loader module code generation.
turbopack/crates/turbopack-ecmascript/src/chunk/item.rs
- Converted arrow functions to traditional function expressions in chunk item code generation.
turbopack/crates/turbopack-ecmascript/src/manifest/loader_module.rs
- Converted arrow functions to traditional function expressions in manifest loader module code generation.

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Code Review

This pull request aims to improve compatibility with older devices by downgrading the generated JavaScript code. The changes systematically replace modern JavaScript features like const, arrow functions, and for...of loops with their older equivalents (var, function expressions, and traditional for loops). A fallback for globalThis is also introduced to support various JavaScript environments. The changes are consistent and effectively achieve the stated goal. My review includes a suggestion to refactor a duplicated constant to improve code maintainability.

gemini-code-assist · 2026-03-17T18:19:32Z

turbopack/crates/turbopack-browser/src/chunking_context.rs

+pub const GLOBAL_THIS_FALLBACK_EXPR: &str =
+    "typeof globalThis !== \"undefined\" ? globalThis : (typeof self !== \"undefined\" ? self : (typeof window !== \"undefined\" ? window : (typeof global !== \"undefined\" ? global : {})))";


This constant is a duplicate of one defined in turbopack-ecmascript-runtime/src/browser_runtime.rs. To avoid duplication, this definition should be removed. The constant in the other crate can be made public and used here instead. The other files in this crate that use this constant will need to update their imports to something like use turbopack_ecmascript_runtime::browser_runtime::GLOBAL_THIS_FALLBACK_EXPR;.

gemini-code-assist · 2026-03-17T18:19:32Z

turbopack/crates/turbopack-ecmascript-runtime/src/browser_runtime.rs

+const GLOBAL_THIS_FALLBACK_EXPR: &str =
+    "typeof globalThis !== \"undefined\" ? globalThis : (typeof self !== \"undefined\" ? self : (typeof window !== \"undefined\" ? window : (typeof global !== \"undefined\" ? global : {})))";


To avoid code duplication, this constant could be made public (pub const) so it can be reused in the turbopack-browser crate. A duplicate of this constant is currently being added in turbopack-browser/src/chunking_context.rs. By making this one public, the other one can be removed.

Suggested change

const GLOBAL_THIS_FALLBACK_EXPR: &str =

"typeof globalThis !== \"undefined\" ? globalThis : (typeof self !== \"undefined\" ? self : (typeof window !== \"undefined\" ? window : (typeof global !== \"undefined\" ? global : {})))";

pub const GLOBAL_THIS_FALLBACK_EXPR: &str =

"typeof globalThis !== \"undefined\" ? globalThis : (typeof self !== \"undefined\" ? self : (typeof window !== \"undefined\" ? window : (typeof global !== \"undefined\" ? global : {})))";

xusd320 · 2026-03-18T06:00:01Z

turbopack/crates/turbopack-ecmascript-runtime/src/browser_runtime.rs


-                const __chunk__ = (() => {{
-                if (!Array.isArray(globalThis["{chunk_loading_global}"])) {{
+                var __chunk__ = (function() {{


为啥选择直接改 runtime 源码？这样如果想打包 es6 都做不到，而且同步上游代码也很烦啊。

上游推荐直接改，这个会同步去上游，后面用个什么配置把这里设置一下:

这里比较麻烦的地方一个在于:

module factory 全是 arrow function，可能会有体积影响

这里还有 async / await 片段(async module load)

TURBOPACK: downgrade insert js code

5396b79

gemini-code-assist bot reviewed Mar 17, 2026

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fireairforce mentioned this pull request Mar 17, 2026

[WIP]feat(pack): downgrade turbopack runtime insert js code utooland/utoo#2707

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xusd320 reviewed Mar 18, 2026

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xusd320 marked this pull request as draft March 18, 2026 07:15

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TURBOPACK: downgrade insert js code#123

TURBOPACK: downgrade insert js code#123
fireairforce wants to merge 1 commit intoutoofrom
downgrade-turbopack-runtime-code

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		pub const GLOBAL_THIS_FALLBACK_EXPR: &str =
		"typeof globalThis !== \"undefined\" ? globalThis : (typeof self !== \"undefined\" ? self : (typeof window !== \"undefined\" ? window : (typeof global !== \"undefined\" ? global : {})))";

		const GLOBAL_THIS_FALLBACK_EXPR: &str =
		"typeof globalThis !== \"undefined\" ? globalThis : (typeof self !== \"undefined\" ? self : (typeof window !== \"undefined\" ? window : (typeof global !== \"undefined\" ? global : {})))";

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