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Simplify a branch of the Awaited type and clean up comments #45918

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Sep 16, 2021
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Simplify a branch of the Awaited type and clean up comments #45918

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12 changes: 5 additions & 7 deletions src/lib/es5.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1477,13 +1477,11 @@ interface Promise<T> {
*/
type Awaited<T> =
T extends null | undefined ? T : // special case for `null | undefined` when not in `--strictNullChecks` mode
T extends object ? // `await` only unwraps object types with a callable then. Non-object types are not unwrapped.
T extends { then(onfulfilled: infer F): any } ? // thenable, extracts the first argument to `then()`
F extends ((value: infer V) => any) ? // if the argument to `then` is callable, extracts the argument
Awaited<V> : // recursively unwrap the value
never : // the argument to `then` was not callable.
T : // argument was not an object
T; // non-thenable
T extends object & { then(onfulfilled: infer F): any } ? // `await` only unwraps object types with a callable `then`. Non-object types are not unwrapped
F extends ((value: infer V) => any) ? // if the argument to `then` is callable, extracts the argument
Awaited<V> : // recursively unwrap the value
never : // the argument to `then` was not callable
T; // non-object or non-thenable

interface ArrayLike<T> {
readonly length: number;
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