/**
 * subscribeKey
 *
 * The subscribeKey utility enables subscription to a primitive subproperty of a given state proxy.
 * Subscriptions created with subscribeKey will only fire when the specified property changes.
 * notifyInSync: same as the parameter to subscribe(); true disables batching of subscriptions.
 *
 * @example
 * import { subscribeKey } from 'valtio/utils'
 * subscribeKey(state, 'count', (v) => console.log('state.count has changed to', v))
 */
export declare function subscribeKey<T extends object, K extends keyof T>(proxyObject: T, key: K, callback: (value: T[K]) => void, notifyInSync?: boolean): () => void;