Bug 209571

Summary:	Function.length broken by Object.defineProperty and bind
Product:	WebKit	Reporter:	Andy Niccolai <andy.niccolai>
Component:	JavaScriptCore	Assignee:	Nobody <webkit-unassigned>
Status:	RESOLVED DUPLICATE
Severity:	Normal	CC:	ashvayka, fpizlo, webkit-bug-importer, ysuzuki
Priority:	P2	Keywords:	InRadar
Version:	Safari Technology Preview
Hardware:	Mac
OS:	macOS 10.15

Description Andy Niccolai 2020-03-25 16:32:50 PDT

With the release of Safari 13.1 (and also verified in 13.2 Technical Preview), Function.length always returns zero after binding arguments to a function that has a custom name defined.

Repro JS Fiddle: https://jsfiddle.net/7s9yop23/

Repro code

const originalFn = (a, b) => a + b;
Object.defineProperty(originalFn, 'name', {value: 'newFunctionName'});
const renamedAndBoundFn = originalFn.bind(undefined, 1);

// expected: 1
// actual: 0
renamedAndBoundFn.length

Comment 1 Radar WebKit Bug Importer 2020-03-25 18:03:41 PDT

<rdar://problem/60898213>

Comment 2 Yusuke Suzuki 2020-03-25 19:07:07 PDT

(In reply to Andy Niccolai from comment #0)
> With the release of Safari 13.1 (and also verified in 13.2 Technical
> Preview), Function.length always returns zero after binding arguments to a
> function that has a custom name defined.
> 
> Repro JS Fiddle: https://jsfiddle.net/7s9yop23/
> 
> Repro code
> 
> const originalFn = (a, b) => a + b;
> Object.defineProperty(originalFn, 'name', {value: 'newFunctionName'});
> const renamedAndBoundFn = originalFn.bind(undefined, 1);
> 
> // expected: 1
> // actual: 0
> renamedAndBoundFn.length

Thanks for reporting!
This is fixed in https://bugs.webkit.org/show_bug.cgi?id=208497 :)

*** This bug has been marked as a duplicate of bug 208497 ***