GeezerVison

What

ArgConverter::CreateJsWrapper only cached prototypes for JS-extended classes (ClassPrototypes). Every other native object returned to JS rebuilt its prototype on each wrap:

• objc_getClass(meta->name())
• the constructor template lookup
• GetFunction
• a new "prototype" V8 string and a property Get

Without extra protocols the constructor template is cached per meta, so its prototype never changes. MetaInstancePrototypes keeps it per meta; a wrap with no extra protocols now goes straight to SetPrototype. Wraps with extra protocols take the existing path.

Behaviour change: native constructor prototypes are read-only

The cache is only correct if C.prototype cannot be replaced, so interface and protocol constructor templates now call ReadOnlyPrototype(), as struct constructors already do since #499. Adding members to a native prototype still works; replacing it does not:

Before, the replacement succeeded but only some instances saw it:

With the cache and a writable prototype, NSUUID.UUID() would have kept the old prototype too, which is the case CodeRabbit flagged. Making the assignment fail keeps every path on the same prototype. TypeScript extends and extend() only read the base prototype, and nothing in the runtime or TestRunner assigns one.

Both tables were checked on the simulator with a probe spec, on the parent commit and on this branch.

Measurements

iPhone 17 Pro simulator, xplat-benchmarks NativeScript app, size M, 5 interleaved rounds. Both builds come from this branch, with and without the cache. attached is the mount phase up to the views being attached, B/A:

Four of five rounds went the same way; one round was noisy in both directions. In a sampled profile of that app, this lookup chain was about 40% of CreateJsWrapper. ReadOnlyPrototype() only runs when a constructor template is created, so it does not affect the wrap path.

Testing

• TestRunner on an iPhone 17 Pro simulator (iOS 26.4): 1836 specs, 0 failures, 11 skipped.
• New ApiTests.js spec: NSMutableArray.prototype is not writable, a strict-mode assignment throws, and a wrapped native instance still gets that prototype and passes instanceof. It restores the prototype afterwards, so a regression fails this spec alone and not every later array test.
• Simulator builds of NativeScript.framework swapped into the benchmark app; every benchmark round ran to completion.

Summary by CodeRabbit

• Performance Improvements
  • Reusing cached prototypes can make repeated creation of native object wrappers more efficient.
• Bug Fixes
  • Native class and protocol prototypes can no longer be replaced, helping ensure native arrays retain their expected type and behavior. Strict-mode attempts to replace a protected prototype now throw an error.