import type { VoidFn } from "../ts/types.js";
export type SignalChange<T> = (next: T, previous?: T) => unknown;
/**
 * Wrapper around a value that allows listening for changes by calling .onValue
 * @example
 * const mySignal = new Signal<number>();
 * mySignal.onValue(console.log);
 *
 * // Set the value
 * mySignal._ = 1;
 *
 * // Read the value
 * mySignal._;
 */
export declare class Signal<T> {
    private value;
    private readonly _observers;
    constructor(value: T, onValue?: SignalChange<T>);
    get _(): T;
    set _(next: T);
    /**
     * @param cb Called after Signal._ is set with new and old values cb(next, previous)
     */
    onValue(cb: SignalChange<T>): VoidFn;
}
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