/**
 * cfcs
 * Copyright (c) 2022-present NAVER Corp.
 * MIT license
 */
import Component from "@egjs/component";
interface EmitterEvents<Value> {
    update: (value: Value, prevValue: Value) => void;
}
/**
 * Creates a mutable ref object. You can access the `.current` value and detect the value change through `.subscribe`.
 * @category Reactive
 * @see observe
 */
export declare class Observer<Value = any> {
    protected _current: Value;
    protected _emitter: Component<EmitterEvents<Value>>;
    /**
     *
     */
    constructor(value?: Value);
    /**
     * return the current value.
     */
    get current(): Value;
    set current(value: Value);
    /**
     * When the current value changes, the callback function is called.
     */
    subscribe(callback: (value: Value, prevValue: Value) => void): this;
    /**
     * Cancel the registered subscription through callback.
     */
    unsubscribe(callback?: (value: Value, prevValue: Value) => void): this;
    protected _setCurrent(value: Value): void;
    /**
     * @hidden
     */
    toString(): string;
    /**
     * @hidden
     */
    valueOf(): Value;
}
export {};