对于Jest, React和TypeScript用户:

我创建了一个mockLocalStorage.ts

export const mockLocalStorage = () => {
  const setItemMock = jest.fn();
  const getItemMock = jest.fn();

  beforeEach(() => {
    Storage.prototype.setItem = setItemMock;
    Storage.prototype.getItem = getItemMock;
  });

  afterEach(() => {
    setItemMock.mockRestore();
    getItemMock.mockRestore();
  });

  return { setItemMock, getItemMock };
};

我的组件:

export const Component = () => {
    const foo = localStorage.getItem('foo')
    localStorage.setItem('bar', 'true')
    return <h1>{foo}</h1>
}

然后在我的测试中，我这样使用它:

import React from 'react';

import { mockLocalStorage } from '../../test-utils';
import { Component } from './Component';

const { getItemMock, setItemMock } = mockLocalStorage();

it('fetches something from localStorage', () => {
    getItemMock.mockReturnValue('bar');
    render(<Component />);
    expect(getItemMock).toHaveBeenCalled();
    expect(getByText(/bar/i)).toBeInTheDocument()
});

it('expects something to be set in localStorage' () => {
    const value = "true"
    const key = "bar"
    render(<Component />);
    expect(setItemMock).toHaveBeenCalledWith(key, value);
}

要在Typescript中做同样的事情，请执行以下步骤:

设置一个包含以下内容的文件:

let localStorageMock = (function() {
  let store = new Map()
  return {

    getItem(key: string):string {
      return store.get(key);
    },

    setItem: function(key: string, value: string) {
      store.set(key, value);
    },

    clear: function() {
      store = new Map();
    },

    removeItem: function(key: string) {
        store.delete(key)
    }
  };
})();
Object.defineProperty(window, 'localStorage', { value: localStorageMock });

然后将以下行添加到包中。json在你的Jest配置

:“setupTestFrameworkScriptFile PATH_TO_YOUR_FILE”,

或者在您想要模拟本地存储的测试用例中导入该文件。

你可以使用这种方法来避免嘲笑。

Storage.prototype.getItem = jest.fn(() => expectedPayload);

答:

目前(7月22日)localStorage不能像你通常会被嘲笑或监视，并在创建-反应-应用程序文档中概述。这是由于jsdom中所做的更改。你可以在jest和jsdom问题跟踪器中读到它。

作为一种变通方法，你可以监视原型:

// does not work:
jest.spyOn(localStorage, "setItem");
localStorage.setItem = jest.fn();

// either of these lines will work, different syntax that does the same thing:
jest.spyOn(Storage.prototype, 'setItem');
Storage.prototype.setItem = jest.fn();

// assertions as usual:
expect(localStorage.setItem).toHaveBeenCalled();

关于监视原型机的注意事项:

监视实例使您能够观察和模拟特定对象的行为。

另一方面，监视原型，将同时观察/操作该类的每个实例。除非您有一个特殊的用例，否则这可能不是您想要的。

但是，在本例中没有区别，因为localStorage只存在一个实例。

首先，我创建了一个名为localStorage.ts(localStorage.js)的文件

class LocalStorageMock {
  store: Store;
  length: number;

  constructor() {
    this.store = {};
    this.length = 0;
  }

  key(n: number): any {
    if (typeof n === 'undefined') {
      throw new Error(
        "Uncaught TypeError: Failed to execute 'key' on 'Storage': 1 argument required, but only 0 present."
      );
    }

    if (n >= Object.keys(this.store).length) {
      return null;
    }

    return Object.keys(this.store)[n];
  }

  getItem(key: string): Store | null {
    if (!Object.keys(this.store).includes(key)) {
      return null;
    }

    return this.store[key];
  }

  setItem(key: string, value: any): undefined {
    if (typeof key === 'undefined' && typeof value === 'undefined') {
      throw new Error(
        "Uncaught TypeError: Failed to execute 'setItem' on 'Storage': 2 arguments required, but only 0 present."
      );
    }

    if (typeof value === 'undefined') {
      throw new Error(
        "Uncaught TypeError: Failed to execute 'setItem' on 'Storage': 2 arguments required, but only 1 present."
      );
    }

    if (!key) return undefined;

    this.store[key] = value.toString() || '';
    this.length = Object.keys(this.store).length;

    return undefined;
  }

  removeItem(key: string): undefined {
    if (typeof key === 'undefined') {
      throw new Error(
        "Uncaught TypeError: Failed to execute 'removeItem' on 'Storage': 1 argument required, but only 0 present."
      );
    }

    delete this.store[key];
    this.length = Object.keys(this.store).length;
    return undefined;
  }

  clear(): undefined {
    this.store = {};
    this.length = 0;

    return undefined;
  }
}

export const getLocalStorageMock = (): any => {
  return new LocalStorageMock();
};

global.localStorage = new LocalStorageMock();

然后创建名为session.test.ts的测试文件(session.test.js)

import { getLocalStorageMock } from '../localstorage';
describe('session storage', () => {
  let localStorage;
  beforeEach(() => {
    localStorage = getLocalStorageMock();
  });

  describe('getItem', () => {
    it('should return null if the item is undefined', () => {
      expect(localStorage.getItem('item')).toBeNull();
    });
    it("should return '' instead of null", () => {
      localStorage.setItem('item', '');
      expect(localStorage.getItem('item')).toBe('');
    });
    it('should return navid', () => {
      localStorage.setItem('item', 'navid');
      expect(localStorage.getItem('item')).toBe('navid');
    });

  });
});

这对我很有效，

delete global.localStorage;
global.localStorage = {
getItem: () => 
 }