对于前端打包构建生产环境的产出内容，特别是在采用了 Vue.js、React 或 Angular 等主流框架的时候，其体积达数 M 是很常见的现象。

当希望对包体积进行优化分析时，或许你知道可以选择使用 webpack-bundle-analyzer， 其实 source-map-explorer 也是个不错的选择。当打包输出结果生成了 sourceMap，source-map-explorer 就可以据此分析出每个模块所占用的体积。而且它不仅限于 JavaScript，对于 Css 预处理器 LESS 和 Sass 来说同样适用。

1 使用 source-map-explorer

1.1 构建输出项目

首先对前端项目构建输出用于生产环境的内容，注意开启 sourceMap 的输出。

1.2 使用 source-map-explorer 分析示例

source-map-explorer 的用法相当简单。首先全局安装 source-map-explorer：

npm i -g source-map-explorer

然后进入打包输出内容目录，执行如下命令（示例中的 为具体产出结果的 hash 值占位符）：

source-map-explorer main.<hash>.js main.<hash>.js.map

你也可以不全局安装它，直接使用 npx 执行：

npx source-map-explorer main.<hash>.js main.<hash>.js.map

如一切正常，该命令会在临时目录生成 html 文件分析结果，并自动打开浏览器进行显示。示例：

以上为单文件分析的简单示例。也可以使用通配符方式，如：

npx source-map-explorer dist/prod/*.js

我们可以将该命令配置到 package.json 的 scripts 脚本中：

{
  "scripts": {
     "analyze": "npx source-map-explorer dist/prod/*.js",
  }
}

在完打包完成之后，执行 npm run analyze 即可得到分析结果。

2 source-map-explorer 功能参数

Analyze and debug space usage through source maps.
Usage:
source-map-explorer script.js [script.js.map] [--json [result.json] | --html [result.html] | --tsv [result.csv]] [-m | --only-mapped] [--exclude-source-map] [--no-bor                                                                                                         der-checks] [--gzip] [--sort] [--replace=BEFORE_1 BEFORE_2 --with=AFTER_1 AFTER_2] [--no-root] [--coverage coverage.json] [--version] [--help | -h]

Output:
  --json  If filename specified save output as JSON to specified file otherwise output to stdout.  [string]
  --tsv   If filename specified save output as TSV to specified file otherwise output to stdout.  [string]
  --html  If filename specified save output as HTML to specified file otherwise output to stdout rather than opening a browser.  [string]

Replace:
  --replace  Apply a simple find/replace on source file names. This can be used to fix some oddities with paths that appear in the source map generation process. Acce                                                                                                         pts regular expressions.  [array]
  --with     See --replace.  [array]

Options:
  --version             Show version number  [boolean]
  --only-mapped, -m     Exclude "unmapped" bytes from the output. This will result in total counts less than the file size  [boolean]
  --exclude-source-map  Exclude source map comment size from output  [boolean]
  --no-root             To simplify the visualization, source-map-explorer will remove any prefix shared by all sources. If you wish to disable this behavior, set --n                                                                                                         o-root.  [boolean]
  --no-border-checks    Disable invalid mapping column/line checks.  [boolean]
  --coverage            If the path to a valid a chrome code coverage JSON export is supplied, the tree map will be colorized according to which percentage of the mod                                                                                                         ules code was executed  [string]
  --gzip                Calculate gzip size. It also sets onlyMapped flag  [boolean]
  --sort                Sort filenames  [boolean]
  -h, --help            Show help  [boolean]

Examples:
  source-map-explorer script.js script.js.map       Explore bundle
  source-map-explorer script.js                     Explore bundle with inline source map
  source-map-explorer dist/js/*.*                   Explore all bundles inside dist/js folder
  source-map-explorer script.js --tsv               Explore and output result as TSV to stdout
  source-map-explorer script.js --json result.json  Explore and save result as JSON to the file

3 更多参考

• https://www.npmjs.com/package/source-map-explorer
• https://www.npmjs.com/package/webpack-bundle-analyzer