fix: minimization issue with Next.js 15+ by ttypic · Pull Request #2059 · ably/ably-js

ttypic · 2025-07-14T15:44:39Z

Related to #2057

SWC that Next.js uses for minimization, inlines functions inside XHRRequest class, that results in losing this context and broken code.

Unfortunately there is no easy way to fix this on the Next.js 15+ side:

Starting with v15, minification cannot be customized using next.config.js.

This PR fixes a single immediate issue. Another problem with other minimizers may appear soon. I’ll create a RFC with code practices we should adopt to avoid this in the future.

Summary by CodeRabbit

Refactor
- Improved the handling of HTTP request state changes for better consistency and reliability.

coderabbitai · 2025-07-14T15:44:46Z

Walkthrough

The change updates the assignment of xhr.onerror, xhr.ontimeout, and xhr.onreadystatechange event handlers from traditional function expressions to arrow functions, ensuring the this context refers to the surrounding class instance without altering the existing handler logic.

Changes

File(s)	Change Summary
src/platform/web/lib/http/request/xhrrequest.ts	Converted `xhr.onerror`, `xhr.ontimeout`, and `xhr.onreadystatechange` handlers from function expressions to arrow functions for lexical `this` binding.

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src/platform/web/lib/http/request/xhrrequest.ts (3 hunks)

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src/platform/web/lib/http/request/xhrrequest.ts

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VeskeR · 2025-07-14T16:17:18Z

    };

-    xhr.onreadystatechange = function () {
+    xhr.onreadystatechange = () => {


also, if function expressions are a problem in SWC minimization, shouldn't we also change xhr.onerror and xhr.ontimeout assignments in this file to also use arrow functions just to be safe?

I looked into minimized code and

a.onerror=function(e){u(e,"XHR error occurred",null,400)}

and

a.ontimeout=function(e){u(e,"Request timed out",null,408)}

it's nothing to inline here. On other hand, here is onreadystatechange:

a.onreadystatechange=function(){let i=a.readyState;i<3||0!==a.status&&(void 0===t&&(t=a.status,(()=>{var s;if(clearTimeout(r),n=t<400,204==t)return this.complete(null,null,null,null,t)...

To fix this properly, we need to decide on a strategy for all function declarations across all SDKs. I think it would be good to release this fix first so SDK users don’t have to wait. This definitely doesn’t introduce any new problems but does fix some existing ones.

I looked into minimized code and
a.onerror=function(e){u(e,"XHR error occurred",null,400)}
and
a.ontimeout=function(e){u(e,"Request timed out",null,408)}

huh, so there are multiple places which call errorHandler so it doesn't get inlined and as a result xhr.onerror and xhr.ontimeout don't break

I mean, changing xhr.onerror and xhr.ontimeout to arrow functions is trivial but if you'd like to keep this PR specific and fix the immediate problem with xhr.onreadystatechange then sure. Will approve the PR as it fixes the problem

Starting with v15, minification cannot be customized using next.config.js. SWC that Next.js uses for minimization, inlines functions inside `XHRRequest` class, that results in losing `this` context and broken code

ttypic requested a review from VeskeR July 14, 2025 15:44

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VeskeR reviewed Jul 14, 2025

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Comment thread src/platform/web/lib/http/request/xhrrequest.ts

VeskeR reviewed Jul 14, 2025

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VeskeR approved these changes Jul 14, 2025

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fix: minimization issue with Next.js 15+

2af70ce

Starting with v15, minification cannot be customized using next.config.js. SWC that Next.js uses for minimization, inlines functions inside `XHRRequest` class, that results in losing `this` context and broken code

ttypic force-pushed the fix-minimization-error branch from 28e365d to 2af70ce Compare July 14, 2025 16:53

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ttypic marked this pull request as draft July 14, 2025 18:19

ttypic marked this pull request as ready for review July 15, 2025 08:51

ttypic merged commit 61e8fc6 into main Jul 15, 2025
10 of 17 checks passed

ttypic deleted the fix-minimization-error branch July 15, 2025 09:14

VeskeR mentioned this pull request Jul 25, 2025

Ably Real-time Connection Fails on Vercel Deployment but Works Locally #2057

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fix: minimization issue with Next.js 15+#2059

fix: minimization issue with Next.js 15+#2059
ttypic merged 1 commit into
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