Support for Object.hasOwn narrowing #71
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acutmore
reviewed
Jun 17, 2022
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| if (isPropertyAccessExpression(callExpression.expression)) { | ||
| const callAccess = callExpression.expression; | ||
| if (isIdentifier(callAccess.name) && callAccess.name.escapedText === "hasOwn" && callExpression.arguments.length === 2 && isStringLiteralLike(callExpression.arguments[1])) { |
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A downside to special casing the exact names here is that it would break for cases where the function is assigned to a different name:
const hasProp = Object.hasOwn;
if (hasProp(o, 'test')) ...I think instead of adding this logic within the compiler itself, we might be able to do it by updating the .d.ts definitions that are packaged with tsc. Something like:
interface ObjectConstructor {
hasOwn<T, P extends string>(o: T, p: P): o is Extract<T, { [p in P]: unknown }>;
}
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Agreed, it seems like we have the necessary building blocks to express this already.
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