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用jsdom开玩笑,文档在Promise解析中未定义

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The scenario

尝试使用Jest(和Enzyme)测试一个简单的React组件 . 这个组件使用 react-dropzone ,我想测试一些涉及DOM的操作,所以我使用jsdom(已经由 create-react-app 配置)

The problem

我的测试代码中可用的 document 对象也可以在组件内部使用,它位于dropzone onDrop 回调内部 undefined ,这会阻止测试运行 .

The code

MyDropzone

import React from 'react'
import Dropzone from 'react-dropzone'

const MyDropzone = () => {
    const onDrop = ( files ) =>{
        fileToBase64({file: files[0]})
            .then(base64Url => {
                return resizeBase64Img({base64Url})
            })
            .then( resizedURL => {
                console.log(resizedURL.substr(0, 50))
            })
    }
    return (
        <div>
            <Dropzone onDrop={onDrop}>
                Some text
            </Dropzone>
        </div>
    );
};

const fileToBase64 = ({file}) => {
    return new Promise((resolve, reject) => {
        const reader = new FileReader()
        reader.onload = () => {
            return resolve(reader.result)
        }
        reader.onerror = (error) => {
            return reject(error)
        }
        reader.readAsDataURL(file)
    })
}

/**
 * Resize base64 image to width and height,
 * keeping the original image proportions
 * with the width winning over the height
 *
 */
const resizeBase64Img = ({base64Url, width = 50}) => {
    const canvas = document.createElement('canvas')
    canvas.width = width
    const context = canvas.getContext('2d')
    const img = new Image()

    return new Promise((resolve, reject) => {
        img.onload = () => {
            const imgH = img.height
            const imgW = img.width
            const ratio = imgW / imgH
            canvas.height = width / ratio
            context.scale(canvas.width / imgW, canvas.height / imgH)
            context.drawImage(img, 0, 0)
            resolve(canvas.toDataURL())
        }

        img.onerror = (error) => {
            reject(error)
        }

        img.src = base64Url
    })
}

export default MyDropzone;

MyDropzone.test.jsx

import React from 'react'
import { mount } from 'enzyme'
import Dropzone from 'react-dropzone'

import MyDropzone from '../MyDropzone'

describe('DropzoneInput component', () => {
    it('Mounts', () => {
        const comp = mount(<MyDropzone />)
        const dz = comp.find(Dropzone)
        const file = new File([''], 'testfile.jpg')
        console.log(document)
        dz.props().onDrop([file])
    })
})

setupJest.js

import { configure } from 'enzyme'
import Adapter from 'enzyme-adapter-react-16'

configure({ adapter: new Adapter() })

Config

  • 默认 create-react-app jest配置, setupJest.js 已添加到 setupFiles

  • 运行:纱线测试

Error

TypeError: Cannot read property 'createElement' of undefined
    at resizeBase64Img (C:\dev\html\sandbox\src\MyDropzone.jsx:44:29)
    at fileToBase64.then.base64Url (C:\dev\html\sandbox\src\MyDropzone.jsx:8:20)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)

More info

考虑到如果在浏览器中运行该代码,则始终定义 document ,因此对我来说问题似乎与jsdom或Jest有关 .

我不确定它是否与Promise,FileReaded或JS范围有关 .

可能是Jest方面的一个错误?

1 回答

  • 6

    所以我能够解决这个问题 . 假设它在没有任何配置更改的情况下工作是错误的 . 首先,您需要添加更多包 . 以下是我更新的 package.json

    {
      "name": "js-cra",
      "version": "0.1.0",
      "private": true,
      "dependencies": {
        "react": "^16.3.2",
        "react-dom": "^16.3.2",
        "react-dropzone": "^4.2.9",
        "react-scripts": "1.1.4",
        "react-test-renderer": "^16.3.2"
      },
      "scripts": {
        "start": "react-scripts start",
        "build": "react-scripts build",
        "test": "react-scripts test",
        "eject": "react-scripts eject"
      },
      "devDependencies": {
        "enzyme": "^3.3.0",
        "enzyme-adapter-react-16": "^1.1.1",
        "jest-enzyme": "^6.0.0",
        "jsdom": "11.10.0",
        "jsdom-global": "3.0.2"
      }
    }
    

    我还从测试脚本中删除了 --env=jsdom . 因为我无法使用这种组合

    之后,您需要创建一个 src/setupTests.js ,它是测试的加载全局变量 . 这个你需要加载 jsdomenzyme

    import { configure } from 'enzyme';
    import Adapter from 'enzyme-adapter-react-16';
    import 'jest-enzyme';
    import 'jsdom-global/register'; //at the top of file , even  , before importing react
    
    configure({ adapter: new Adapter() });
    

    之后,您的测试会出错并出现以下错误

    /Users/tarun.lalwani/Desktop/tarunlalwani.com/tarunlalwani/workshop/ub16/so/jsdom-js-demo/node_modules/react-scripts/scripts/test.js:20
      throw err;
      ^
    
    ReferenceError: FileReader is not defined
    

    问题似乎是 FileReader 应该引用 window 范围 . 所以你需要像下面这样更新它

    const reader = new window.FileReader()
    

    然后再次运行测试

    Working tests

    现在测试工作正常

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