65 lines
1.6 KiB
Plaintext
65 lines
1.6 KiB
Plaintext
/**
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Get the element type of an `Iterable`/`AsyncIterable`. For example, `Array`, `Set`, `Map`, generator, stream, etc.
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This can be useful, for example, if you want to get the type that is yielded in a generator function. Often the return type of those functions are not specified.
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This type works with both `Iterable`s and `AsyncIterable`s, so it can be use with synchronous and asynchronous generators.
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Here is an example of `IterableElement` in action with a generator function:
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@example
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```
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import type {IterableElement} from 'type-fest';
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function * iAmGenerator() {
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yield 1;
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yield 2;
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}
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type MeNumber = IterableElement<ReturnType<typeof iAmGenerator>>
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```
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And here is an example with an async generator:
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@example
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```
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import type {IterableElement} from 'type-fest';
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async function * iAmGeneratorAsync() {
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yield 'hi';
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yield true;
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}
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type MeStringOrBoolean = IterableElement<ReturnType<typeof iAmGeneratorAsync>>
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```
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Many types in JavaScript/TypeScript are iterables. This type works on all types that implement those interfaces.
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An example with an array of strings:
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@example
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```
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import type {IterableElement} from 'type-fest';
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type MeString = IterableElement<string[]>
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```
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@example
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```
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import type {IterableElement} from 'type-fest';
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const fruits = new Set(['🍎', '🍌', '🍉'] as const);
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type Fruit = IterableElement<typeof fruits>;
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//=> '🍎' | '🍌' | '🍉'
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```
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@category Iterable
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*/
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export type IterableElement<TargetIterable> =
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TargetIterable extends Iterable<infer ElementType> ?
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ElementType :
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TargetIterable extends AsyncIterable<infer ElementType> ?
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ElementType :
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never;
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