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javascript - Webpack 使用 Emscripten 引发错误：无法解析 'fs'

问题描述

我在将 javascript 文件导入 vue.js 组件时遇到错误：

这是 /components 子文件夹的内容：

/startingV/src/components$ ls -lah
total 132K
drwxr-xr-x 2 marco marco 4,0K dic 26 11:22 .
drwxr-xr-x 5 marco marco 4,0K dic 26 09:32 ..
-rw-r--r-- 1 marco marco  441 nov  2  2016 Counter.vue
-rw-r--r-- 1 marco marco  441 dic 21 15:13 FormValidation.vue
-rw-r--r-- 1 marco marco 100K dic 26 10:38 js_plumbing.js
-rw-r--r-- 1 marco marco 9,3K dic 26 10:38 js_plumbing.wasm
-rw-r--r-- 1 marco marco  473 dic 26 11:14 Result.vue

编译时：

Failed to compile.

./src/components/js_plumbing.js
Module not found: Error: Can't resolve 'fs' in '/home/marco/cpp/WebAssemblyinAction
/Appendix_B/B.1_ccall/startingV/src/components'

这是 Result.vue 文件：

template>
    <p button @click="callAdd">Add!</p>
</template>

<script>
    import * as js_plumbing from './js_plumbing'
    export default {
      data () {
        return {
          result: null
        }
      },
      methods: {
        callAdd() {
          const result = Module.ccall('js_plumbing.Add',
              'number',
              ['number', 'number'],
              [1, 2]);
          console.log('Result: ${result}');
        }
      }
    }
</script>

js_plumbing.js 和 js_plumbing.wasm 文件是通过这个命令生成的： 

emcc add.c -o js_plumbing.js -s EXTRA_EXPORTED_RUNTIME_METHODS=['ccall','cwrap']

其中 add.c 是：

#include <stdlib.h>
#include <emscripten.h>

// If this is an Emscripten (WebAssembly) build then...
#ifdef __EMSCRIPTEN__
  #include <emscripten.h>
#endif

#ifdef __cplusplus
extern "C" { // So that the C++ compiler does not rename our function names
#endif

EMSCRIPTEN_KEEPALIVE
int Add(int value1, int value2) 
{
  return (value1 + value2); 
}

#ifdef __cplusplus
}
#endif

这是我获取有关如何生成 .js 和 .wasm 文件的一些信息的链接： https ://emscripten.org/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.html#interacting-with-code-ccall-包裹

执行 npn run dev 时命令行中的完整错误消息：

(base) marco@marco-U36SG:~/cpp/WebAssemblyinAction/Appendix_B 
/B.1_ccall/startingV$ npm run dev

> myproject@1.0.0 dev /home/marco/cpp/WebAssemblyinAction/Appendix_B 
/B.1_ccall/startingV
> cross-env NODE_ENV=development webpack-dev-server --open --hot

✖ ｢wdm｣: Hash: 12bee4de7abfde1cbc5d
Version: webpack 4.41.3
Time: 6707ms
Built at: 12/26/2019 12:37:07 PM
   Asset      Size  Chunks                    Chunk Names
build.js  2.18 MiB    main  [emitted]  [big]  main
Entrypoint main [big] = build.js
[0] multi (webpack)-dev-server/client?http://localhost:8080   
(webpack)/hot/dev-server.js ./src/main.js 52 bytes {main} [built]
[./node_modules/strip-ansi/index.js] 161 bytes {main} [built]
[./node_modules/vue/dist/vue.esm.js] 319 KiB {main} [built]
[./node_modules/webpack-dev-server/client/index.js?http:
//localhost:8080] (webpack)-dev-server/client?http://localhost:8080  
4.29 KiB {main} [built]
[./node_modules/webpack-dev-server/client/overlay.js] (webpack)-dev-
server/client/overlay.js 3.51 KiB {main} [built]
[./node_modules/webpack-dev-server/client/socket.js] (webpack)-dev-
server/client/socket.js 1.53 KiB {main} [built]
[./node_modules/webpack-dev-server/client/utils/createSocketUrl.js]   
(webpack)-dev-server/client/utils/createSocketUrl.js 2.89 KiB {main} 
[built]
[./node_modules/webpack-dev-server/client/utils/log.js] (webpack)-dev-
server/client/utils/log.js 964 bytes {main} [built]
[./node_modules/webpack-dev-server/client/utils/reloadApp.js] 
(webpack)-dev-server/client/utils/reloadApp.js 1.59 KiB {main} [built]
[./node_modules/webpack-dev-server/client/utils/sendMessage.js] 
(webpack)-dev-server/client/utils/sendMessage.js 402 bytes {main}   
[built]
[./node_modules/webpack/hot sync ^\.\/log$] (webpack)/hot sync 
nonrecursive ^\.\/log$ 170 bytes {main} [built]
[./node_modules/webpack/hot/dev-server.js] (webpack)/hot/dev-server.js
 1.59 KiB {main} [built]
[./node_modules/webpack/hot/emitter.js] (webpack)/hot/emitter.js 75 
bytes {main} [built]
[./node_modules/webpack/hot/log-apply-result.js] (webpack)/hot/log-
apply-result.js 1.27 KiB {main} [built]
[./src/main.js] 134 bytes {main} [built]
    + 34 hidden modules

ERROR in ./src/components/js_plumbing.js
Module not found: Error: Can't resolve 'fs' in '/home/marco 
/cpp/WebAssemblyinAction/Appendix_B/B.1_ccall/startingV
/src/components'
 @ ./src/components/js_plumbing.js 88:26-39
 @ ./node_modules/babel-loader/lib!./node_modules/vue-loader
/lib/selector.js?type=script&index=0!./src/components/Result.vue
 @ ./src/components/Result.vue
 @ ./node_modules/babel-loader/lib!./node_modules/vue-loader
/lib/selector.js?type=script&index=0!./src/App.vue
 @ ./src/App.vue
 @ ./src/main.js

如何解决？马可

标签： javascriptvue.jsmodulewebassemblyemscripten

解决方案

TLDR；

有两种解决方案：

  1. 添加-s ENVIRONMENT='web'你的 emcc 命令，所以试试emcc add.c -o js_plumbing.js -s EXTRA_EXPORTED_RUNTIME_METHODS=['ccall','cwrap'] -s ENVIRONMENT='web'

或者

  1. "node": { "fs": "empty" }在您的webpack.config.js. 我不知道如何以零配置方式做到这一点。

为什么

Emscripten 的 emcc 命令同时生成.js和.wasm文件。该.js文件不仅是 的包装器，.wasm而且还为 Web 提供了 C/C++ 运行时，更重要的是，在问题中，它是.wasm文件的通用加载器。

该.js文件的加载器非常全面，默认涵盖了 node、web、web worker 和D8 JS shell。这通常会给 Webpack 等捆绑器带来问题，因为捆绑器会尝试解析源代码中的所有模块，包括require('fs')用于.wasm在 nodejs 环境中加载文件的模块，并且如果任何模块不适用于 Web 环境，则捆绑器会产生错误。

避免该问题的一种方法是在命令中使用ENVIRONMENT标志。emcc这将删除一些有问题的代码，例如require('fs').

fs另一种方法是通过添加"node": { "fs": "empty" }webpack 配置让 Webpack 忽略模块。

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