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Polyfill TypedArray.slice() in older browsers. fixes #11008 #11011

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Polyfill TypedArray.slice() in older browsers. fixes #11008 #11011

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d62293d
Polyfill TypedArray.slice() in older browsers. fixes #11008
kripken Apr 27, 2020
0bc1aee
enable test too, and fix
kripken Apr 27, 2020
cebe6cf
prefer subarray over Array.prototype
kripken Apr 28, 2020
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15 changes: 15 additions & 0 deletions src/runtime_init_memory.js
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Original file line number Diff line number Diff line change
Expand Up @@ -91,3 +91,18 @@ HEAP32[DYNAMICTOP_PTR>>2] = DYNAMIC_BASE;
#if USE_PTHREADS
}
#endif

#if MIN_CHROME_VERSION < 45 || MIN_EDGE_VERSION < 14 || MIN_FIREFOX_VERSION < 38 || MIN_IE_VERSION != TARGET_NOT_SUPPORTED
// Older browsers may lack TypedArray.slice()
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/slice#Browser_compatibility
[Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array,
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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.

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Interesting, thanks, I didn't know that.

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

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

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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

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

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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?

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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.

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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).

Float32Array, Float64Array].forEach(function(typedArray) {
if (!typedArray.prototype.slice) {
Object.defineProperty(typedArray.prototype, 'slice', {
value: function(begin, end) {
return new typedArray(this.subarray(begin, end));
}
});
}
});
#endif
2 changes: 0 additions & 2 deletions tests/test_other.py
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Expand Up @@ -3436,8 +3436,6 @@ def test(expected, opts=[]):
# when legacy is needed, we show an error indicating so
test('build with LEGACY_VM_SUPPORT')
# legacy + disabling wasm works
if self.is_wasm_backend():
return
test('hello, world!', ['-s', 'LEGACY_VM_SUPPORT=1', '-s', 'WASM=0'])

def test_on_abort(self):
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