# 故障處理
Webpack 的配置比較復雜，很容出現錯誤，下面是一些通常的故障處理手段。
一般情況下，webpack 如果出問題，會打印一些簡單的錯誤信息，比如模塊沒有找到。我們還可以通過參數 `--display-error-details` 來打印錯誤詳情。
```bash
$ webpack --display-error-details
Hash: a40fbc6d852c51fceadb
Version: webpack 1.12.2
Time: 586ms
Asset Size Chunks Chunk Names
bundle.js 12.1 kB 0 [emitted] main
[0] ./entry.js 153 bytes {0} [built] [1 error]
[5] ./module.js 43 bytes {0} [built]
+ 4 hidden modules
ERROR in ./entry.js
Module not found: Error: Cannot resolve 'file' or 'directory' ./badpathmodule in /Users/zhaoda/data/projects/webpack-handbook/examples
resolve file
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule doesn't exist
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.webpack.js doesn't exist
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.js doesn't exist
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.web.js doesn't exist
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.json doesn't exist
resolve directory
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule doesn't exist (directory default file)
/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule/package.json doesn't exist (directory description file)
[/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule]
[/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.webpack.js]
[/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.js]
[/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.web.js]
[/Users/zhaoda/data/projects/webpack-handbook/examples/badpathmodule.json]
@ ./entry.js 3:0-26
```
Webpack 的配置提供了 `resolve` 和 `resolveLoader` 參數來設置模塊解析的處理細節，`resolve` 用來配置應用層的模塊（要被打包的模塊）解析，`resolveLoader` 用來配置 `loader` 模塊的解析。
當引入通過 npm 安裝的 node.js 模塊時，可能出現找不到依賴的錯誤。Node.js 模塊的依賴解析算法很簡單，是通過查看模塊的每一層父目錄中的 `node_modules` 文件夾來查詢依賴的。當出現 Node.js 模塊依賴查找失敗的時候，可以嘗試設置 `resolve.fallback` 和 `resolveLoader.fallback` 來解決問題。
```js
module.exports = {
resolve: { fallback: path.join(__dirname, "node_modules") },
resolveLoader: { fallback: path.join(__dirname, "node_modules") }
};
```
Webpack 中涉及路徑配置最好使用絕對路徑，建議通過 `path.resolve(__dirname, "app/folder")` 或 `path.join(__dirname, "app", "folder")` 的方式來配置，以兼容 Windows 環境。
