Object.defineProperty(window, "localStorage", {
  value: {
    getItem: jest.fn(),
    setItem: jest.fn(),
    removeItem: jest.fn(),
  },
});

or

jest.spyOn(Object.getPrototypeOf(localStorage), "getItem");
jest.spyOn(Object.getPrototypeOf(localStorage), "setItem");

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。

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);
}

正如@ck4所建议的那样，文档已经清楚地解释了如何使用localStorage。然而，模拟函数无法执行任何localStorage方法。

下面是我的react组件的详细示例，它使用抽象方法来写入和读取数据，

//file: storage.js
const key = 'ABC';
export function readFromStore (){
    return JSON.parse(localStorage.getItem(key));
}
export function saveToStore (value) {
    localStorage.setItem(key, JSON.stringify(value));
}

export default { readFromStore, saveToStore };

错误:

TypeError: _setupLocalStorage2.default.setItem is not a function

解决办法: 为jest添加以下mock函数(路径:.jest/mocks/setUpStore.js)

let mockStorage = {};

module.exports = window.localStorage = {
  setItem: (key, val) => Object.assign(mockStorage, {[key]: val}),
  getItem: (key) => mockStorage[key],
  clear: () => mockStorage = {}
};

Snippet从这里引用

在这个网站的帮助下，我们找到了答案:https://groups.google.com/forum/#!主题/ jestjs / 9 ephunwvytg

设置一个包含以下内容的文件:

var localStorageMock = (function() {
  var store = {};
  return {
    getItem: function(key) {
      return store[key];
    },
    setItem: function(key, value) {
      store[key] = value.toString();
    },
    clear: function() {
      store = {};
    },
    removeItem: function(key) {
      delete store[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”,

这对我来说是可行的，只需要一行代码

const setItem = jest.spyOn(Object.getPrototypeOf(localStorage)， 'setItem');