Webpack：source-map的正确使用方式

source-map

阮一峰老师对source-map的讲解

source-map对我们有什么帮助？

当我们在使用webpack这类打包工具的时候，通常打包出来的文件都是经过压缩混淆的，在debugger的过程中很难调试，看到的代码都是压缩过后的浏览器无法辨别。而通过source-map定位到源代码，方便我们调试。

由于项目代码是私密的，所以建议开发环境开启source-map，线上环境关闭，线上需要排查问题的话可以将source-map上传到错误监控系统。

如何开启source-map

开启source-map只需要在webpack.config.js中指定

module.exports = {
   devtool: "source-map"
}

source-map的分类

eval

eval类型的source-map在文件末尾执行源文件的位置。

使用eval类型的source-map

module.exports = {
   devtool: "eval"
}

打包出来的结果：


/***/ "./src/pages/index/index.js":
/***/ (function(module, exports) {
eval("\n\n//# sourceURL=webpack:///./src/pages/index/index.js?");
/***/ })
/******/ });

可以看出直接在eval文件中指定了source-map

source-map

source-map类型会生成一个.map文件

使用source-map类型的source-map

module.exports = {
   devtool: "source-map"
}

打包结果：

/***/ "./src/pages/about/index.js":
/***/ (function(module, exports) {
/***/ })
/******/ });
//# sourceMappingURL=about.js.map

上面结果看出在最后指定了一个.map文件，来看一下这个文件有什么。

{
  "version": 3,
  "sources": ["webpack:///webpack/bootstrap"],
  "names": [],
  "mappings": ";QAAA;QACA;;QAEA;QACA;;QAEA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;;QAEA;QACA;;QAEA;QACA;;QAEA;QACA;QACA;;;QAGA;QACA;;QAEA;QACA;;QAEA;QACA;QACA;QACA,0CAA0C,gCAAgC;QAC1E;QACA;;QAEA;QACA;QACA;QACA,wDAAwD,kBAAkB;QAC1E;QACA,iDAAiD,cAAc;QAC/D;;QAEA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;QACA;QACA,yCAAyC,iCAAiC;QAC1E,gHAAgH,mBAAmB,EAAE;QACrI;QACA;;QAEA;QACA;QACA;QACA,2BAA2B,0BAA0B,EAAE;QACvD,iCAAiC,eAAe;QAChD;QACA;QACA;;QAEA;QACA,sDAAsD,+DAA+D;;QAErH;QACA;;;QAGA;QACA",
  "file": "about.js",
  "sourcesContent": [
    " \t// The module cache\n \tvar installedModules = {};\n\n \t// The require function\n \tfunction __webpack_require__(moduleId) {\n\n \t\t// Check if module is in cache\n \t\tif(installedModules[moduleId]) {\n \t\t\treturn installedModules[moduleId].exports;\n \t\t}\n \t\t// Create a new module (and put it into the cache)\n \t\tvar module = installedModules[moduleId] = {\n \t\t\ti: moduleId,\n \t\t\tl: false,\n \t\t\texports: {}\n \t\t};\n\n \t\t// Execute the module function\n \t\tmodules[moduleId].call(module.exports, module, module.exports, __webpack_require__);\n\n \t\t// Flag the module as loaded\n \t\tmodule.l = true;\n\n \t\t// Return the exports of the module\n \t\treturn module.exports;\n \t}\n\n\n \t// expose the modules object (__webpack_modules__)\n \t__webpack_require__.m = modules;\n\n \t// expose the module cache\n \t__webpack_require__.c = installedModules;\n\n \t// define getter function for harmony exports\n \t__webpack_require__.d = function(exports, name, getter) {\n \t\tif(!__webpack_require__.o(exports, name)) {\n \t\t\tObject.defineProperty(exports, name, { enumerable: true, get: getter });\n \t\t}\n \t};\n\n \t// define __esModule on exports\n \t__webpack_require__.r = function(exports) {\n \t\tif(typeof Symbol !== 'undefined' && Symbol.toStringTag) {\n \t\t\tObject.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });\n \t\t}\n \t\tObject.defineProperty(exports, '__esModule', { value: true });\n \t};\n\n \t// create a fake namespace object\n \t// mode & 1: value is a module id, require it\n \t// mode & 2: merge all properties of value into the ns\n \t// mode & 4: return value when already ns object\n \t// mode & 8|1: behave like require\n \t__webpack_require__.t = function(value, mode) {\n \t\tif(mode & 1) value = __webpack_require__(value);\n \t\tif(mode & 8) return value;\n \t\tif((mode & 4) && typeof value === 'object' && value && value.__esModule) return value;\n \t\tvar ns = Object.create(null);\n \t\t__webpack_require__.r(ns);\n \t\tObject.defineProperty(ns, 'default', { enumerable: true, value: value });\n \t\tif(mode & 2 && typeof value != 'string') for(var key in value) __webpack_require__.d(ns, key, function(key) { return value[key]; }.bind(null, key));\n \t\treturn ns;\n \t};\n\n \t// getDefaultExport function for compatibility with non-harmony modules\n \t__webpack_require__.n = function(module) {\n \t\tvar getter = module && module.__esModule ?\n \t\t\tfunction getDefault() { return module['default']; } :\n \t\t\tfunction getModuleExports() { return module; };\n \t\t__webpack_require__.d(getter, 'a', getter);\n \t\treturn getter;\n \t};\n\n \t// Object.prototype.hasOwnProperty.call\n \t__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };\n\n \t// __webpack_public_path__\n \t__webpack_require__.p = \"\";\n\n\n \t// Load entry module and return exports\n \treturn __webpack_require__(__webpack_require__.s = \"./src/pages/about/index.js\");\n"
  ],
  "sourceRoot": ""
}

.map文件中存储的关于源文件的一些信息，并且在sourcesContent属性中存储这源文件代码。

inline-source-map

inline-source-map会将source-map的信息内联进打包出来的文件。

使用inline-source-map类型的source-map

module.exports = {
   devtool: "inline-source-map"
}

打包结果：

/***/ "./src/pages/about/index.js":
/***/ (function(module, exports) {

/***/ })
/******/ });
//# sourceMappingURL=data:application/json;charset=utf-8;base64,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

由打包文件看到，source-map的信息被内联到了文件中。

cheap-source-map

cheap-source-map类型当定位报错的时候只能定位到行，不能定位到列，也就是说不能准确的定位到是哪个地方报错。

使用cheap-source-map类型的source-map

module.exports = {
   devtool: "cheap-source-map"
}

打包的内容和source-map类型基本相同，只是.map文件有些区别。

hubvue / webpack-learn