[kpal81xd]

Description

Hot reloading with swap never worked for ESM (.mjs) scripts. Saving an edited script left the old code running and swap was never called. Two things stopped it:

• The loader cache. The script handler deletes its cache entry so an edited script loads again. For ESM scripts it deleted the entry under the URL with its query removed, which isn't the key the loader stored it under. The entry stayed, and the next load returned the old result without reaching the handler.
• The module map. The browser keeps an imported module for the life of the page, so importing the same URL again returns the old module.

This PR:

• deletes the loader cache entry under the key it was stored with;
• imports a module script by its plain URL the first time, as now, so scripts that import each other still share one module (ESM Preload Fix #7161);
• imports it with ?t=<file hash> only when the file has been edited since then, so the new code runs, re-registers its script types and fires swap.

Only the edited file is evaluated again. Modules that import it, or that it imports, keep their existing instances, and its top-level code runs again. Each edit keeps one more module instance in memory until the page reloads. Published builds don't change their files at runtime, so they are unaffected.

Fixes playcanvas/editor#1337
Part of playcanvas/editor#1115

Manual smoke test

1. In an Editor project using this engine, add an ESM script with a swap(old) method and an update that rotates its entity, and attach it to an entity.
2. Launch the scene.
3. Change the rotation speed in update and save.

Expected: the launched app rotates at the new speed without a refresh, and swap is called.

Checklist

• I have read the contributing guidelines
• My code follows the project's coding standards
• This PR focuses on a single change

[github-actions]

Public API report

This PR changes the public API surface (+1 / −1), per the docs' rules (@ignore / @Private / undocumented are excluded).

Show API diff

-ScriptHandler.load(url: any, callback: any): void
+ScriptHandler.load(url: any, callback: any, asset: any): void

Informational only — this never fails the build.

[github-actions]

Build size report

This PR changes the size of the minified bundles.

Bundle	Minified	Gzip	Brotli
playcanvas.min.js	2829.4 KB (+142 B, +0.00%)	736.6 KB (+63 B, +0.01%)	570.3 KB (+255 B, +0.04%)
playcanvas.min.mjs	2826.1 KB (+142 B, +0.00%)	734.7 KB (+50 B, +0.01%)	569.3 KB (−281 B, −0.05%)

[kpal81xd]

Tested in the Editor with a launched scene. The scene has one entity using an ESM script with a swap method, and each edit changes the script's file the way saving it does.

Engine	After saving an edited ESM script	Script type running	swap called
2.23.3	The launch page received the new file	The old version	Never
This PR	Two edits in a row	Updated to each new version, on the registry and the live instance	Once per edit

initialize was not called again, and there were no console errors.

Not tested: typing in the code editor itself (the edits were saved programmatically), and browsers other than Chrome.