Polyfill TypedArray.slice() in older browsers. fixes #11008

[kripken]

Also enable LEGACY_VM_SUPPORT on wasm backend testing,
which was disabled for some reason.

[JustAMan]

@kripken Mozilla-provided polyfill hard-crashed in WebOS 1.2 emulator (where I found the issue). The engine just died restarting app from scratch.

I've ended up just taking older code from yours like this: https://github.com/jellyfin/JavascriptSubtitlesOctopus/blob/master/src/pre-worker.js#L10-L17

[sbc100]

WebOS 1.2 emulator! I've not heard that name in maybe a decade. What JS engine is running in there?

[kripken]

Ok, I changed it to use this.subarray as in that link - please let me know if that works.

[JustAMan]

I've not heard that name in maybe a decade.

That's a bit strange, my TV has WebOS 2.0 and was manufactured in 2015. So it's not exactly recent, but it has a decent 4K panel and passive 3D, so I would still like to continue using it. Same could be said about WebOS 1.2 devices - they still have nice panels, and attaching an external TV box is a hassle as it usually adds one more remote to manage the device.

What JS engine is running in there?

navigator.userAgent says "Mozilla/5.0 (Web0S; Linux i686) AppleWebKit/537.41 (KHTML, like Gecko) Large Screen WebAppManager Safari/537.41".
But those engines are real funky, e.g. engine in WebOS 2.0 claims it supports Promises but chokes on Promise.resolve() wanting Promise.resolve(undefined) instead, etc.

[JustAMan]

I think it should be good. Also it seems to have been lost, needs a nudge probably?

[RReverser]

Note that all of those actually have a super-class TypedArray that is not directly exposed. That is, instead of adding a method to each and every class, you can get a TypedArray reference via

var typedArrayProto = Int8Array.prototype.__proto__;

and then polyfill typedArrayProto.slice once.

[kripken]

Interesting, thanks, I didn't know that.

Do you know if that's well-supported in all legacy browsers?

[RReverser]

I don't, unfortunately, and can't test it.

[dmitrylyzo]

Still relevant. In fact, we need these polyfills.

Tested this polyfill:

var typedArrayProto = Object.getPrototypeOf(Int8Array.prototype);
if (typedArrayProto && !typedArrayProto.slice) {
    typedArrayProto.slice = function (begin, end) {
        return new this.constructor(this.subarray(begin, end));
    }
}

webOS 1.2 (WebKit)
Polyfill works correctly.

Object.getPrototypeOf(Int8Array.prototype):     [object ArrayBufferViewPrototype]
Int8Array.prototype:                            [object Int8ArrayPrototype]
Object.getPrototypeOf(Int8Array):               [object Object]
Int8Array:                                      [object Int8ArrayConstructor]

Object.getPrototypeOf(Int32Array.prototype):    [object ArrayBufferViewPrototype]
Int32Array.prototype:                           [object Int32ArrayPrototype]
Object.getPrototypeOf(Int32Array):              [object Object]
Int32Array:                                     [object Int32ArrayConstructor]

Object.getPrototypeOf(Int8Array.prototype) === Object.getPrototypeOf(Int32Array.prototype): true
Object.getPrototypeOf(Int8Array.prototype) === Object.getPrototypeOf({}): false

webOS 3 (Chrome 38)
Polyfill works, but {} gets slice. So it is probably better to leave as it is.

Object.getPrototypeOf(Int8Array.prototype):     [object Object]
Int8Array.prototype:                            [object Object]
Object.getPrototypeOf(Int8Array):               function Empty() {}
Int8Array:                                      function Int8Array() { [nativecode] }

Object.getPrototypeOf(Int32Array.prototype):    [object Object]
Int32Array.prototype:                           [object Object]
Object.getPrototypeOf(Int32Array):              function Empty() {}
Int32Array:                                     function Int32Array() { [nativecode] }

Object.getPrototypeOf(Int8Array.prototype) === Object.getPrototypeOf(Int32Array.prototype): true
Object.getPrototypeOf(Int8Array.prototype) === Object.getPrototypeOf({}): true

[kripken]

@dmitrylyzo thanks for the info. Would you like to open a PR that takes this code and updates it to use the right polyfills?

[dmitrylyzo]

I tested your polyfill - works fine. As I said, I think it is better (for legacy browsers) than the super-class polyfill, because in webOS 3 super-class polyfill adds slice to every object due to a common prototype (but it could just be a glitch of the emulator).

As for the other polyfills, they are for the libraries used in that project. Wouldn't their inclusion bloat the output file?

[sbc100]

Can I ask what targets do you have that run webOS 3 (chrome 38). That seems like a rather old version of the browser to target.

[dmitrylyzo]

Mostly old TVs (https://webostv.developer.lge.com/discover/specifications/web-engine/). Jellyfin is targeting Chrome 27 as a rough approximation of webOS 1.2 and 2.0 (both WebKit).

[kripken]

I think this is blocked on getting confirmation that it works. @JustAMan did you get a chance to verify that? (Would also be good to verify @RReverser 's suggestion as well, as if that works too it sounds better.)

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 30 days. Feel free to re-open at any time if this issue is still relevant.