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import type { Stores, StoresValues } from "svelte/store";
import { derived } from "svelte/store";
import { safeOnDestroy } from "./lifecycle";
import { noop } from "./noop";
type EffectOptions = {
/**
* Whether to skip the first run
* @default undefined
*/
skipFirstRun?: boolean;
};
/**
* A utility function that creates an effect from a set of stores and a function.
* The effect is automatically cleaned up when the component is destroyed.
*
* @template S - The type of the stores object
* @param stores - The stores object to derive from
* @param fn - The function to run when the stores change
* @param opts {@link EffectOptions}
* @returns A function that can be used to unsubscribe the effect
*/
export function effect<S extends Stores>(
stores: S,
fn: (values: StoresValues<S>) => (() => void) | void,
opts: EffectOptions = {}
): () => void {
const { skipFirstRun } = opts;
let isFirstRun = true;
let cb: (() => void) | void = undefined;
// Create a derived store that contains the stores object and an onUnsubscribe function
const destroy = derived(stores, stores => {
cb?.();
if (isFirstRun && skipFirstRun) {
isFirstRun = false;
} else {
cb = fn(stores);
}
}).subscribe(noop);
const unsub = () => {
destroy();
cb?.();
};
// Automatically unsubscribe the effect when the component is destroyed
safeOnDestroy(unsub);
return unsub;
}
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