react-use/tests/useLocalStorage.test.ts

import useLocalStorage from "../src/useLocalStorage";
import "jest-localstorage-mock";
import { renderHook, act } from "@testing-library/react-hooks";

describe(useLocalStorage, () => {
  afterEach(() => localStorage.clear());
  it("retrieves an existing value from localStorage", () => {
    localStorage.setItem("foo", "bar");
    const { result } = renderHook(() => useLocalStorage("foo"));
    const [state] = result.current;
    expect(state).toEqual("bar");
  });
  it("sets initial state", () => {
    const { result } = renderHook(() => useLocalStorage("foo", "bar"));
    const [state] = result.current;
    expect(state).toEqual("bar");
    expect(localStorage.__STORE__["foo"]).toEqual("bar");
  });
  it("prefers existing value over initial state", () => {
    localStorage.setItem("foo", "bar");
    const { result } = renderHook(() => useLocalStorage("foo", "baz"));
    const [state] = result.current;
    expect(state).toEqual("bar");
  });
  it("does not clobber existing localStorage with initialState", () => {
    localStorage.setItem('foo', 'bar')
    const { result } = renderHook(() => useLocalStorage('foo', 'buzz'));
    result.current; // invoke current to make sure things are set
    expect(localStorage.__STORE__['foo']).toEqual('bar');
  })
  it("correctly updates localStorage", () => {
    const { result, rerender } = renderHook(() => useLocalStorage("foo", "bar"));

    const [, setFoo] = result.current;
    act(() => setFoo("baz"));
    rerender();

    expect(localStorage.__STORE__["foo"]).toEqual("baz");
  });
  it("correctly and promptly returns a new value", () => {
    const { result, rerender } = renderHook(() => useLocalStorage("foo", "bar"));

    const [, setFoo] = result.current;
    act(() => setFoo("baz"));
    rerender();

    const [foo] = result.current;
    expect(foo).toEqual("baz");
  });
  it("should not double-JSON-stringify stringy values", () => {
    const { result, rerender } = renderHook(() => useLocalStorage("foo", "bar"));

    const [, setFoo] = result.current;
    act(() => setFoo(JSON.stringify("baz")));
    rerender();

    const [foo] = result.current;
    expect(foo).not.toMatch(/\\/i); // should not contain extra escapes
    expect(foo).toBe('baz');
  });
  it("keeps multiple hooks accessing the same key in sync", () => {
    localStorage.setItem("foo", "bar");
    const { result: r1, rerender: rerender1 } = renderHook(() => useLocalStorage("foo"));
    const { result: r2, rerender: rerender2 } = renderHook(() => useLocalStorage("foo"));

    const [, setFoo] = r1.current;
    act(() => setFoo("potato"));
    rerender1();
    rerender2();

    const [val1] = r1.current;
    const [val2] = r2.current;

    expect(val1).toEqual(val2);
    expect(val1).toEqual("potato");
    expect(val2).toEqual("potato");
  });
  it("parses out objects from localStorage", () => {
    localStorage.setItem("foo", JSON.stringify({ ok: true }));
    const { result } = renderHook(() => useLocalStorage<{ ok: boolean }>("foo"));
    const [foo] = result.current;
    expect(foo.ok).toEqual(true);
  });
  it("safely initializes objects to localStorage", () => {
    const { result } = renderHook(() => useLocalStorage<{ ok: boolean }>("foo", { ok: true }));
    const [foo] = result.current;
    expect(foo.ok).toEqual(true);
  });
  it("safely sets objects to localStorage", () => {
    const { result, rerender } = renderHook(() => useLocalStorage<{ ok: any }>("foo", { ok: true }));

    const [, setFoo] = result.current;
    act(() => setFoo({ ok: "bar" }));
    rerender();

    const [foo] = result.current;
    expect(foo.ok).toEqual("bar");
  });
  it("safely returns objects from updates", () => {
    const { result, rerender } = renderHook(() => useLocalStorage<{ ok: any }>("foo", { ok: true }));

    const [, setFoo] = result.current;
    act(() => setFoo({ ok: "bar" }));
    rerender();

    const [foo] = result.current;
    expect(foo).toBeInstanceOf(Object);
    expect(foo.ok).toEqual("bar");
  });
  it("sets localStorage from the function updater", () => {
    const { result, rerender } = renderHook(() =>
      useLocalStorage<{ foo: string; fizz?: string }>("foo", { foo: "bar" })
    );

    const [, setFoo] = result.current;
    act(() => setFoo(state => ({ ...state, fizz: "buzz" })));
    rerender();

    const [value] = result.current;
    expect(value.foo).toEqual("bar");
    expect(value.fizz).toEqual("buzz");
  });
  describe("raw setting", () => {
    it('returns a string when localStorage is a stringified object', () => {
      localStorage.setItem('foo', JSON.stringify({ fizz: 'buzz' }));
      const { result } = renderHook(() => useLocalStorage('foo', null, true));
      const [foo] = result.current;
      expect(typeof foo).toBe('string');
    });
    it('returns a string after an update', () => {
      localStorage.setItem('foo', JSON.stringify({ fizz: 'buzz' }));
      const { result, rerender } = renderHook(() => useLocalStorage('foo', null, true));

      const [,setFoo] = result.current;
      act(() => setFoo({ fizz: 'bang' }))
      rerender();

      const [foo] = result.current;
      expect(typeof foo).toBe('string');
      expect(JSON.parse(foo)).toBeInstanceOf(Object);
      expect(JSON.parse(foo).fizz).toEqual('bang');
    });
    it('still forces setState to a string', () => {
      localStorage.setItem('foo', JSON.stringify({ fizz: 'buzz' }));
      const { result, rerender } = renderHook(() => useLocalStorage('foo', null, true));

      const [,setFoo] = result.current;
      act(() => setFoo({ fizz: 'bang' }))
      rerender();

      const [value] = result.current;
      expect(JSON.parse(value).fizz).toEqual('bang');
    });
  });
});