babel-plugin-import

一、认识

---

提示

Babel 转换网址

AST 转换网址

babel-plugin-import

二、通过 babel-plugin-import 按需引入 lodash

---

2.1 准备

1. 安装lodash、babel-loader、@babel/core、babel-plugin-import 依赖

   yarn add babel-loader @babel/core babel-plugin-import -D 
   
   yarn add lodash -S

2.2 常规引入 lodash

1. webpack.config.js 配置如下 (不使用任何 loader):

   const Path = require('path');
   
   module.exports = {
       mode: "development",
       entry: Path.resolve(process.cwd(), "./src/index.js"),
       output: {
           filename: "index.js",
           path: Path.resolve(process.cwd(), "./build/"),
       },
   };

2. 入口文件引入 lodash

   import { flatten, concat } from "lodash";
   
   console.log(flatten, concat);

3. 执行webapck build 进行打包编译，编译结果如图所示:

   

   Preview

   如图所示: 只有两句话而已，但是打包出的文件体积巨大。因为他把真个 lodash 文件都打包了，所以我们需要按需引入，减小打包文件的体积

2.3 按需引入 lodash -- babel.config.js

1. webpack.config.js 配置 babel-loader 如下:

   {
       test: /\.js$/,
       use: {
           loader: "babel-loader",
       },
   },

2. webpack.config.js 完整配置如下:

   const Path = require("path");
   
   module.exports = {
       mode: "development",
       entry: Path.resolve(process.cwd(), "./src/index.js"),
       output: {
           filename: "index.js",
           path: Path.resolve(process.cwd(), "./build/"),
       },
       module: {
           rules: [
               {
                   test: /\.js$/,
                   use: {
                   loader: "babel-loader",
                   },
               },
           ],
       },
   };

3. babel.config.js 配置如下:

   module.exports = {
       plugins: [
           [
               "import",
               {
                   libraryName: "lodash",
                   libraryDirectory: "",
               },
           ],
       ],
   };

4. 入口文件引入 lodash

   import { flatten, concat } from "lodash";
   
   console.log(flatten, concat);

5. 执行webapck build 进行打包编译，编译结果如图所示:

   

   Preview

   如图所示: 打包出来的文件体积一下子变得小了许多

2.4 按需引入 lodash -- webpack.config.js

1. webpack.config.js 配置 babel-loader 如下:

   {
       test: /\.js$/,
       use: {
         loader: 'babel-loader',
         options: {
           plugins: [
             [
               "import", {
                 libraryName: "lodash",
                 libraryDirectory: "",
               },
             ],
           ],
         },
       },
     }

2. webpack.config.js 完整代码如下:

   const Path = require('path');
   
   module.exports = {
       mode: "development",
       entry: Path.resolve(process.cwd(), "./src/index.js"),
       output: {
           filename: "index.js",
           path: Path.resolve(process.cwd(), "./build/"),
       },
       module: {
           rules: [
               {
                   test: /\.js$/,
                   use: {
                   loader: 'babel-loader',
                   options: {
                       plugins: [
                           [
                               "import", {
                               libraryName: "lodash",
                               libraryDirectory: "",
                               },
                           ],
                       ],
                   },
                   },
               },
           ],
       },
   };

3. 入口文件引入 lodash

   import { flatten, concat } from "lodash";
   
   console.log(flatten, concat);

4. 执行webapck build 进行打包编译，编译结果如图所示:

   

   Preview

   如图所示: 打包出来的文件体积一下子变得小了许多

三、通过指定路径引入所需 lodash 模块来实现按需引入

---

1. webapck.config.js 配置如下(关闭所有 loader):

   const Path = require("path");
   
   module.exports = {
       mode: "development",
       entry: Path.resolve(process.cwd(), "./src/index.js"),
       output: {
           filename: "index.js",
           path: Path.resolve(process.cwd(), "./build/"),
       },
       module: {
           rules: [
           ],
       },
   };

2. 入口文件分别指定路径引入所需模块

   // import { flatten, concat } from "lodash";
   
   import flatten from 'lodash/flatten';
   import concat from 'lodash/concat';
   
   console.log(flatten, concat);

3. 执行webapck build 进行打包编译，编译结果如图所示:

   

   Preview

   如图所示: 打包出来的文件体积跟babel-plugin-import效果是一样的。

四、通过自己实现的 babel-plugin-import 按需引入 lodash

---

通过指定路径引入所需 lodash 模块来实现按需引入的引入模块方案，我们可以知道所谓的按需引入，就是将import {flatten,concat} from "lodash" 转换为 import flatten from "lodash/flatten" 和 import concat from "lodash/concat"

4.1 不同引入模块方式的 AST 对比

import {flatten,concat} from "lodash" AST 结构:

Preview

import flatten from "lodash/flatten" import concat from "lodash/concat" AST 结构:

Preview

4.2 实现

1. 根目录/plugins/babel-plugin-import.js 编写插件

   const BabelCore = require("@babel/core");
   const Types = require("babel-types");
   
   const babelPluginImport = {
       visitor: {
           ImportDeclaration: {
               enter(nodePath, state = { }) {
                   const { specifiers, source } = nodePath.node;
                   if (
                       state.opts.libraryName === "lodash"
                       && !Types.isImportDefaultSpecifier(specifiers[0])
                   ) {
                       const importDeclarations = specifiers.map((specifier) => Types.importDeclaration(
                           [Types.importDefaultSpecifier(specifier.local)],
                           Types.stringLiteral(`${source.value}/${specifier.local.name}`),
                           ));
                       nodePath.replaceWithMultiple(importDeclarations);
                   }
               },
           },
       },
   };
   
   module.exports = function () {
       return babelPluginImport;
   };

2. webpack.config.js 中配置babel-loader,使用自定义插件

   const Path = require("path");
   
   module.exports = {
       mode: "development",
       devtool: false,
       entry: Path.resolve(process.cwd(), "./src/index.js"),
       output: {
           filename: "index.js",
           path: Path.resolve(process.cwd(), "./build/"),
       },
       module: {
           rules: [
           {
               test: /\.js$/,
               use: {
                   loader: "babel-loader",
                   options: {
                       plugins: [
                       [
                           Path.resolve(process.cwd(), './plugins/babel-plugin-import.js'),
                           {
                               libraryName: 'lodash',
                           },
                       ],
                       ],
                   },
               },
           },
           ],
       },
   };

3. 执行webapck build 进行打包编译，编译结果如图所示:

   

   Preview

   如图所示: 打包出来的文件体积跟babel-plugin-import效果是一样的。