svelte/packages/svelte/src/internal/client/hydratable.js

import { async_mode_flag } from '../flags/index.js';
import { hydrating } from './dom/hydration.js';
import * as w from './warnings.js';
import * as e from './errors.js';
import { DEV } from 'esm-env';

/**
 * @template T
 * @param {string} key
 * @param {() => T} fn
 * @returns {T}
 */
export function hydratable(key, fn) {
	if (!async_mode_flag) {
		e.experimental_async_required('hydratable');
	}

	if (!hydrating) {
		return fn();
	}

	const store = window.__svelte?.h;
	if (!store?.has(key)) {
		hydratable_missing_but_expected(key);
		return fn();
	}

	return /** @type {T} */ (store.get(key));
}

/** @param {string} key */
function hydratable_missing_but_expected(key) {
	if (DEV) {
		e.hydratable_missing_but_required(key);
	} else {
		w.hydratable_missing_but_expected(key);
	}
}