Promise Interop

toSignal converts a Promise<T> to a signal getter.

import { toSignal } from "@kayahr/signal";

const value = toSignal(Promise.resolve(1));

value();   // undefined while pending, then 1
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Options

Without options, the returned getter yields undefined until the promise fulfills. Its type is therefore Getter<T | undefined>.

initialValue

Use initialValue when the signal should expose a concrete value while the promise is pending.

const count = toSignal(Promise.resolve(1), {
    initialValue: 0
});
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Until the promise fulfills, count() returns 0. The getter type is Getter<number> instead of Getter<number | undefined>.

equals

equals works exactly like it does for signals, memos, and resources. By default, toSignal uses Object.is.

Use a custom equality function when the fulfilled value should only replace the initial value if a meaningful part changed.

const user = toSignal(loadUser(), {
    initialValue: cachedUser,
    equals: (previous, next) => previous.id === next.id
});
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Set equals to false when fulfillment should always count as a change, even if the fulfilled value compares equal to the initial value.

Error Handling

Promise rejections are stored and rethrown when the signal getter is read. Nothing is thrown directly from the asynchronous rejection callback.

Disposal

The returned getter can be manually disposed with dispose(...) and is also registered on the active scope, if there is one. A promise cannot be canceled, but its fulfillment or rejection is ignored after disposal.

import { dispose } from "@kayahr/scope";
import { toSignal } from "@kayahr/signal";

const value = toSignal(loadValue());

dispose(value);
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