@zeix/ui-element/src/core/context.d.ts

UIElement - minimal reactive framework based on Web Components

import { UIElement, type ComponentSignals } from "../ui-element";
/** @see https://github.com/webcomponents-cg/community-protocols/blob/main/proposals/context.md */
/**
 * A context key.
 *
 * A context key can be any type of object, including strings and symbols. The
 *  Context type brands the key type with the `__context__` property that
 * carries the type of the value the context references.
 */
type Context<K, V> = K & {
    __context__: V;
};
/**
 * An unknown context type
 */
type UnknownContext = Context<unknown, unknown>;
/**
 * A helper type which can extract a Context value type from a Context type
 */
type ContextType<T extends UnknownContext> = T extends Context<string, infer V> ? V : never;
/**
 * A callback which is provided by a context requester and is called with the value satisfying the request.
 * This callback can be called multiple times by context providers as the requested value is changed.
 */
type ContextCallback<V> = (value: V, unsubscribe?: () => void) => void;
declare global {
    interface HTMLElementEventMap {
        /**
         * A 'context-request' event can be emitted by any element which desires
         * a context value to be injected by an external provider.
         */
        'context-request': ContextRequestEvent<Context<string, unknown>>;
    }
}
declare const CONTEXT_REQUEST = "context-request";
/**
 * Class for context-request events
 *
 * An event fired by a context requester to signal it desires a named context.
 *
 * A provider should inspect the `context` property of the event to determine if it has a value that can
 * satisfy the request, calling the `callback` with the requested value if so.
 *
 * If the requested context event contains a truthy `subscribe` value, then a provider can call the callback
 * multiple times if the value is changed, if this is the case the provider should pass an `unsubscribe`
 * function to the callback which requesters can invoke to indicate they no longer wish to receive these updates.
 *
 * @class ContextRequestEvent
 * @extends {Event}
 *
 * @property {T} context - context key
 * @property {ContextCallback<ContextType<T>>} callback - callback function for value getter and unsubscribe function
 * @property {boolean} [subscribe=false] - whether to subscribe to context changes
 */
declare class ContextRequestEvent<T extends UnknownContext> extends Event {
    readonly context: T;
    readonly callback: ContextCallback<ContextType<T>>;
    readonly subscribe: boolean;
    constructor(context: T, callback: ContextCallback<ContextType<T>>, subscribe?: boolean);
}
/**
 * Initialize context provider / consumer for a UIElement instance
 *
 * @since 0.9.0
 * @param {UIElement} host - UIElement instance to initialize context for
 * @return {boolean} - true if context provider was initialized successfully, false otherwise
 */
declare const useContext: <S extends ComponentSignals>(host: UIElement<S>) => boolean;
export { type Context, type UnknownContext, CONTEXT_REQUEST, ContextRequestEvent, useContext };