Array.prototype[Symbol.unscopables] is not a function

TypeScript Version: 3.7.0-dev.20191018

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Code

const x = [][Symbol.unscopables];
console.log(x.copyWithin);

const y = [][Symbol.unscopables]();
console.log(y.copyWithin);

Expected behavior:
x.copyWithin occurs no error, and [][Symbol.unscopables]() occurs type error.

Actual behavior:
x.copyWithin occurs type error, and [][Symbol.unscopables]() occurs runtime exception.

Playground Link:
http://www.typescriptlang.org/play/?ts=Nightly&ssl=6&ssc=1&pln=1&pc=1#code/MYewdgzgLgBAHjAvDA2gXRQZQJ4FsBGIANgHQCukoADgIb5ECmEaA3ALABQokxDJRIAOYAKOCWrYA6gEsoAC2lgAlOw6du0GNiSoMOAsXKUQtekzTCV68BF78hw7OJNTZC5aqA

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