27 lines
1.1 KiB
TypeScript
27 lines
1.1 KiB
TypeScript
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import type { LitElement } from 'lit';
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type UpdateHandler = (prev?: unknown, next?: unknown) => void;
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type NonUndefined<A> = A extends undefined ? never : A;
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type UpdateHandlerFunctionKeys<T extends object> = {
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[K in keyof T]-?: NonUndefined<T[K]> extends UpdateHandler ? K : never;
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}[keyof T];
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interface WatchOptions {
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/**
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* If true, will only start watching after the initial update/render
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*/
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waitUntilFirstUpdate?: boolean;
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}
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/**
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* Runs when observed properties change, e.g. @property or @state, but before the component updates. To wait for an
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* update to complete after a change occurs, use `await this.updateComplete` in the handler. To start watching after the
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* initial update/render, use `{ waitUntilFirstUpdate: true }` or `this.hasUpdated` in the handler.
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*
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* Usage:
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*
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* @watch('propName')
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* handlePropChange(oldValue, newValue) {
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* ...
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* }
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*/
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export declare function watch(propertyName: string | string[], options?: WatchOptions): <ElemClass extends LitElement>(proto: ElemClass, decoratedFnName: UpdateHandlerFunctionKeys<ElemClass>) => void;
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export {};
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