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Svelte Stores Deep Dive — Advanced Store Patterns

DodaTech Updated 2026-06-28 1 min read

In this tutorial, you will learn about Svelte Stores Deep Dive. We cover key concepts, practical examples, and best practices to help you master this topic.

Svelte stores support advanced patterns including custom stores with encapsulated methods, store composition, derived stores with multiple dependencies, and readable stores for external data.

What You'll Learn

  • Custom stores with methods
  • Readable stores for async data
  • Store composition and chaining
  • Derived stores with multiple inputs
  • Store subscription management

Why It Matters

Advanced store patterns let you encapsulate complex state logic (API syncing, undo/redo, optimistic updates) into reusable, testable store modules.

// stores/todoStore.js
import { writable, derived } from "svelte/store";

function createTodoStore() {
  const todos = writable([]);
  const { subscribe, set, update } = todos;

  return {
    subscribe,
    add(text) {
      update(t => [...t, { id: Date.now(), text, done: false }]);
    },
    toggle(id) {
      update(t => t.map(i => i.id === id ? { ...i, done: !i.done } : i));
    },
    remove(id) {
      update(t => t.filter(i => i.id !== id));
    },
    clearCompleted() {
      update(t => t.filter(i => !i.done));
    },
    async load() {
      const res = await fetch("/api/todos");
      set(await res.json());
    },
  };
}

export const todos = createTodoStore();

export const activeTodos = derived(todos, $t => $t.filter(t => !t.done));
export const completedTodos = derived(todos, $t => $t.filter(t => t.done));
export const stats = derived(todos, $t => ({
  total: $t.length,
  active: $t.filter(t => !t.done).length,
  completed: $t.filter(t => t.done).length,
}));

Expected output: A custom todo store with add, toggle, remove, clearCompleted methods and derived stores for filtered views and statistics.

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