Function update

packages/svelte/src/internal/client/reactivity/sources.js:299–307

(source, d = 1)

 * @returns {T}
 */
export function update(source, d = 1) {
	var value = get(source);
	var result = d === 1 ? value++ : value--;

	set(source, value);

	// @ts-expect-error
	return result;
}

/**
 * @template {number | bigint} T