当项目不仅仅包含.js或.json文件，还包含其他类型文件(如.ts、.vue、.css)作为模块时，配置resolve.extensions可以不必要的文件搜索提高性能。

src/index.ts
import { someFuction } from './module'someFuction()

src/module.tsimport {otherSomeFuction} from './othermodule'export const someFuction = otherSomeFuction

src/othermodule.ts
export const otherSomeFuction = () => {console.log('otherSomeFuction...')
}

优化前

webpack.config.jsconst config = {entry: './src/index.ts',output: {filename: 'main.js'},mode: 'development',resolve: {  extensions: [ '.js', '.json', '.jsx', '.tsx', '.ts'], },  module: {rules: [{test: /\.ts$/,loader: 'ts-loader'}]}
}module.exports = config;

优化后

webpack.config.jsconst config = {entry: './src/index.ts',output: {filename: 'main.js'},mode: 'development',resolve: {  extensions: [ '.ts', '.tsx', '.js', '.jsx', '.json'], },  module: {rules: [{test: /\.ts$/,loader: 'ts-loader'}]}
}module.exports = config;

可以看到优化resolve.extensions的顺序，简单的三个小模块的打包就带来了1508-1467=41ms的性能提升