热重新加载会破坏应用程序。最终加载程序没有返回 Buffer 或 String答案

【问题标题】：Hot reloading breaks the app. Final loader didn't return a Buffer or String热重新加载会破坏应用程序。最终加载程序没有返回 Buffer 或 String
【发布时间】：2019-05-29 15:42:38
【问题描述】：

我有一个自定义加载器，它加载以下文件data.js

  const data = {
    a: ()=> 8885555,
    b: ()=> 55555
  }

  module.exports = name => {
    return data[name] && data[name]()
  }

当我更改上述文件时，例如更改 b 值时，应用程序会中断

ERROR in ../data.js?name=a
Module build failed: Error: Final loader (../data-loader.js) didn't return a Buffer or String
    at runLoaders (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\webpack\lib\NormalModule.js:319:18)
    at C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:373:3
    at iterateNormalLoaders (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:214:10)
    at iterateNormalLoaders (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:221:10)
    at C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:236:3
    at runSyncOrAsync (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:124:12)
    at iterateNormalLoaders (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:232:2)
    at Array.<anonymous> (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\loader-runner\lib\LoaderRunner.js:205:4)
    at Storage.finished (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\enhanced-resolve\lib\CachedInputFileSystem.js:43:16)
    at provider (C:\Users\010\Saber.js\webpack-hmr-3-ways\middleware\node_modules\enhanced-resolve\lib\CachedInputFileSystem.js:79:9)
 @ ./index.js 1:10-40
 @ multi webpack-hot-middleware/client?path=/__webpack_hmr&timeout=20000 ./index.js

这是自定义的 webpack 加载器

const devalue = require('devalue')
const vm = require('vm');

module.exports = async function(source, map) {
    const callback = this.async()
    this.addDependency(this.resourcePath);
    const sandbox = {
        require,
        module
    }
    vm.createContext(sandbox);
    const mod = vm.runInContext(source, sandbox)
    const result = await mod(this.resourceQuery.replace('?name=', ''))
    return callback(null, `export default ${devalue(result)}`, map);
}

这里是复制repo

【问题讨论】：

标签： javascript webpack webpack-hot-middleware

【解决方案1】：

所以这是应该做的

const devalue = require('devalue')
const vm = require('vm');

module.exports = async function(source, map) {
    const callback = this.async()
    this.addDependency(this.resourcePath);
    const sandbox = {
        require,
        module: {exports: {}}
    }
    vm.createContext(sandbox);
    const mod = vm.runInContext(source, sandbox)
    const result = await mod(this.resourceQuery.replace('?name=', ''))
    return callback(null, `export default ${devalue(result)}`, map);
}

问题是我用data.js 文件module.exports 覆盖了加载程序module.exports，因为我将相同的module 传递给sandbox，所以当热重新加载加载程序中的导出函数时被替换为不返回字符串的data.js 函数（在这种情况下，因为data[name] 将是undefined），这就是错误的原因

【讨论】：