How to mock localStorage in JavaScript unit tests?

Question

Are there any libraries out there to mock localStorage?

I\'ve been using Sinon.JS for most of my other javascript mocking and have found it is really gr

Answer 1

credits to https://medium.com/@armno/til-mocking-localstorage-and-sessionstorage-in-angular-unit-tests-a765abdc9d87 Make a fake localstorage, and spy on localstorage, when it is caleld

 beforeAll( () => {
    let store = {};
    const mockLocalStorage = {
      getItem: (key: string): string => {
        return key in store ? store[key] : null;
      },
      setItem: (key: string, value: string) => {
        store[key] = `${value}`;
      },
      removeItem: (key: string) => {
        delete store[key];
      },
      clear: () => {
        store = {};
      }
    };

    spyOn(localStorage, 'getItem')
      .and.callFake(mockLocalStorage.getItem);
    spyOn(localStorage, 'setItem')
      .and.callFake(mockLocalStorage.setItem);
    spyOn(localStorage, 'removeItem')
      .and.callFake(mockLocalStorage.removeItem);
    spyOn(localStorage, 'clear')
      .and.callFake(mockLocalStorage.clear);
  })

And here we use it

it('providing search value should return matched item', () => {
    localStorage.setItem('defaultLanguage', 'en-US');

    expect(...
  });