How to mock localStorage in JavaScript unit tests?

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Here is a simple way to mock it with Jasmine:

let localStore;

beforeEach(() => {
  localStore = {};

  spyOn(window.localStorage, 'getItem').and.callFake((key) =>
    key in localStore ? localStore[key] : null
  );
  spyOn(window.localStorage, 'setItem').and.callFake(
    (key, value) => (localStore[key] = value + '')
  );
  spyOn(window.localStorage, 'clear').and.callFake(() => (localStore = {}));
});

If you want to mock the local storage in all your tests, declare the beforeEach() function shown above in the global scope of your tests (the usual place is a specHelper.js script).

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