Bug 301711

Summary:

Top-level await is broken

Product:

WebKit

Reporter:

Nico Hörter <nico.m.hoerter>

Component:

JavaScriptCore

Assignee:

Nobody <webkit-unassigned>

Status:

RESOLVED DUPLICATE

Severity:

Major

CC:

keith_miller, syg

Priority:

Version:

Safari 26

Hardware:

iPhone / iPad

OS:

iOS 26

Attachments:

Description	Flags
index.html, script.js and x.js files, showing the problem	none

Nico Hörter

Reported 2025-10-30 13:14:14 PDT

Created attachment 477239 [details] index.html, script.js and x.js files, showing the problem When a module with top-level await is imported in multiple script tags, the second import freezes indefinitely and never completes execution. Test Case: The issue can be reproduced with the following minimal test case: index.html: <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <script type="module" src="x.js"></script> <script type="module" src="script.js"></script> <title>Document</title> </head> <body> <h1>The next line should display a number after 1 sec.:</h1> </body> </html> script.js: import { x } from './x.js'; const span = document.createElement('span'); console.log('this will be displayed'); span.textContent = x.toString(); // freeze at this line, because of x import console.log('this will never be displayed'); document.body.appendChild(span); // span will never be displayed x.js: await new Promise(resolve => { setTimeout(() => { resolve(undefined); }, 1000); }); // export after top level await export const x = 10; Expected Behavior: After approximately 1 second, the console should display both log messages ("this will be displayed" and "this will never be displayed"), and the number "10" should appear on the page. The module x.js should only execute its top-level await once, and all imports should receive the resolved module. Actual Behavior: 1. Only "this will be displayed" appears in the console 2. The execution in script.js freezes at the line span.textContent = x.toString() 3. The second console.log never executes 4. The span is never appended to the document 5. No error is thrown

Attachments
index.html, script.js and x.js files, showing the problem (1.06 KB, application/x-zip-compressed) 2025-10-30 13:14 PDT, Nico Hörter	no flags	Details
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Shu-yu Guo

Comment 1 2025-10-30 15:15:00 PDT

Thank you for the report, this is another manifestation of the known TLA issue. *** This bug has been marked as a duplicate of bug 242740 ***

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