四月八日

module.exports = {
  module:{
    rules:[{
      test:/\.js$/,
      use:['my-loader','my-loader1','my-loader2']
    }]
  },
  mode:'production',
  // webpack5 提供resolveLoader可以配置loader的查找目录
  resolveLoader: {
    modules: ['node_modules',path.resolve(__dirname,'loader')],
  },
}

// 同步方法在loader解析时执行
// 也就是use数组中的loader从右向左执行
module.exports = function(content){
  console.log(111);
  return content;
}
// pitch 方法在loader加载时执行
// 也就是use数组中的loader从左向右执行
module.exports.pitch = function(){
  console.log('p111')
}

module.exports = function(content){
  this.callback(null,content);
}

module.exports = function(content){
  var callback = this.async();
  setTimeout(()=>{
    callback(null,content)
  },3000)
}

{
module.exports = {
  module:{
    rules:[{
      test:/\.js$/,
      use:[{
         loader:'my-loader',
         options:{
          test:'1231'
         }        
      },'my-loader1','my-loader2']
    }]
  }
}

const  { getOptions }  = require('loader-utils');
const  { validate }  = require('schema-utils');

const schema = {
  type: 'object',
  properties: {
    test: {
      type: 'string',
    }
  }
};

module.exports = function(content){
  const options = getOptions(this);

  console.log(options);
  validate(schema, options, {
    // 需要校验的loader名称
    name: 'my-loader',
    baseDataPath: 'options',
  });

  this.callback(null,content);
}

const path = require('path');

module.exports = {
  module:{
    rules:[{
      test:/\.js$/,
      loader:'babelLoader',
      options:{
        "presets": ["@babel/preset-env"]
      }
    }]
  },
  mode:'production',
  resolveLoader: {
    modules: ['node_modules',path.resolve(__dirname,'loader')],
  },
}

const  { getOptions }  = require('loader-utils');
const  { validate }  = require('schema-utils');
const {promisify} = require('util')
const babel = require('@babel/core');

const schema = {
  type: 'object',
  properties: {
    persets:{
      type:'array'
    }
  }
};

module.exports = function(content){
  const options = getOptions(this);
  const callback = this.async();

  validate(schema, options, {
    // 需要校验的loader名称
    name: 'babelLoader',
    baseDataPath: 'options',
  });

  console.log(options);


  const transfrom =  promisify(babel.transform);
  transfrom(content,options)
    .then(({code}) =>callback(null,code))
}

{
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"   // 弹出配置文件，操作不可逆
  }
}

{
  "scripts": {
    "start": "node scripts/start.js",
    "build": "node scripts/build.js",
    "test": "node scripts/test.js"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "babel": {
    "presets": [
      "react-app"
    ]
  }dd
}

const path = require('path');
const fs = require('fs');
const getPublicUrlOrPath = require('react-dev-utils/getPublicUrlOrPath');

// Make sure any symlinks in the project folder are resolved:
// https://github.com/facebook/create-react-app/issues/637

// process.cwd() 当前Node.js进程执行时的工作目录  /home/supreme/Dropbox/Workspace/cra-learn/config
// 项目根路径
const appDirectory = fs.realpathSync(process.cwd());
//path.resolve() 方法将路径或路径片段的序列解析为绝对路径。
const resolveApp = relativePath => path.resolve(appDirectory, relativePath);

// We use `PUBLIC_URL` environment variable or "homepage" field to infer
// "public path" at which the app is served.
// webpack needs to know it to put the right <script> hrefs into HTML even in
// single-page apps that may serve index.html for nested URLs like /todos/42.
// We can't use a relative path in HTML because we don't want to load something
// like /todos/42/static/js/bundle.7289d.js. We have to know the root.

// 分析publicUrl路径 默认是"/"
const publicUrlOrPath = getPublicUrlOrPath(
  process.env.NODE_ENV === 'development',
  require(resolveApp('package.json')).homepage,
  process.env.PUBLIC_URL
);

// 打包路径
const buildPath = process.env.BUILD_PATH || 'build';

// 文件扩展名
const moduleFileExtensions = [
  'web.mjs',
  'mjs',
  'web.js',
  'js',
  'web.ts',
  'ts',
  'web.tsx',
  'tsx',
  'json',
  'web.jsx',
  'jsx',
];

// Resolve file paths in the same order as webpack
// appIndexJs: resolveModule(resolveApp, 'src/index')
const resolveModule = (resolveFn, filePath) => {
  // 判断存不存在有这样扩展名的文件
  const extension = moduleFileExtensions.find(extension =>
    fs.existsSync(resolveFn(`${filePath}.${extension}`))
  );
  // 返回文件的绝对路径
  if (extension) {
    return resolveFn(`${filePath}.${extension}`);
  }
  // 默认返回js文件
  return resolveFn(`${filePath}.js`);
};

// Do this as the first thing so that any code reading it knows the right env.
// 声明环境变量
process.env.BABEL_ENV = 'development';
process.env.NODE_ENV = 'development';

// Makes the script crash on unhandled rejections instead of silently
// ignoring them. In the future, promise rejections that are not handled will
// terminate the Node.js process with a non-zero exit code.
process.on('unhandledRejection', err => {
  throw err;
});

// Ensure environment variables are read.
// 引入env配置文件
require('../config/env');


const fs = require('fs');
const chalk = require('react-dev-utils/chalk');
const webpack = require('webpack');
const WebpackDevServer = require('webpack-dev-server');
const clearConsole = require('react-dev-utils/clearConsole');
const checkRequiredFiles = require('react-dev-utils/checkRequiredFiles');
const {
  choosePort,
  createCompiler,
  prepareProxy,
  prepareUrls,
} = require('react-dev-utils/WebpackDevServerUtils');
const openBrowser = require('react-dev-utils/openBrowser');
const semver = require('semver');
const paths = require('../config/paths');
const configFactory = require('../config/webpack.config');
const createDevServerConfig = require('../config/webpackDevServer.config');
const getClientEnvironment = require('../config/env');
const react = require(require.resolve('react', { paths: [paths.appPath] }));

const env = getClientEnvironment(paths.publicUrlOrPath.slice(0, -1));
const useYarn = fs.existsSync(paths.yarnLockFile);
const isInteractive = process.stdout.isTTY;

// Warn and crash if required files are missing
if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
  process.exit(1);
}

// Tools like Cloud9 rely on this.
const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;
const HOST = process.env.HOST || '0.0.0.0';

if (process.env.HOST) {
  console.log(
    chalk.cyan(
      `Attempting to bind to HOST environment variable: ${chalk.yellow(
        chalk.bold(process.env.HOST)
      )}`
    )
  );
  console.log(
    `If this was unintentional, check that you haven't mistakenly set it in your shell.`
  );
  console.log(
    `Learn more here: ${chalk.yellow('https://cra.link/advanced-config')}`
  );
  console.log();
}

// We require that you explicitly set browsers and do not fall back to
// browserslist defaults.
const { checkBrowsers } = require('react-dev-utils/browsersHelper');
// 选择端口号，当端口冲突的时候回自动加一
checkBrowsers(paths.appPath, isInteractive)
  .then(() => {
    // We attempt to use the default port but if it is busy, we offer the user to
    // run on a different port. `choosePort()` Promise resolves to the next free port.
    return choosePort(HOST, DEFAULT_PORT);
  })
  .then(port => {
    if (port == null) {
      // We have not found a port.
      return;
    }
    
    // 核心文件通过configFactory创建
    const config = configFactory('development');
    const protocol = process.env.HTTPS === 'true' ? 'https' : 'http';
    const appName = require(paths.appPackageJson).name;
    // 是否存在ts配置文件，判断是否启用TS
    const useTypeScript = fs.existsSync(paths.appTsConfig);
    const tscCompileOnError = process.env.TSC_COMPILE_ON_ERROR === 'true';
    const urls = prepareUrls(
      protocol,
      HOST,
      port,
      paths.publicUrlOrPath.slice(0, -1)
    );

    const devSocket = {
      warnings: warnings =>
        devServer.sockWrite(devServer.sockets, 'warnings', warnings),
      errors: errors =>
        devServer.sockWrite(devServer.sockets, 'errors', errors),
    };
    // Create a webpack compiler that is configured with custom messages.
    // 创建webpack编译器
    const compiler = createCompiler({
      appName,
      config,
      devSocket,
      urls,
      useYarn,
      useTypeScript,
      tscCompileOnError,
      webpack,
    });
    // Load proxy config
    // 创建代理配置信息
    const proxySetting = require(paths.appPackageJson).proxy;
    const proxyConfig = prepareProxy(
      proxySetting,
      paths.appPublic,
      paths.publicUrlOrPath
    );
    // Serve webpack assets generated by the compiler over a web server.
    // 创建server服务器配置
    const serverConfig = createDevServerConfig(
      proxyConfig,
      urls.lanUrlForConfig
    );
    // 创建服务器并监听端口
    const devServer = new WebpackDevServer(compiler, serverConfig);
    // Launch WebpackDevServer.
    devServer.listen(port, HOST, err => {
      if (err) {
        return console.log(err);
      }
      if (isInteractive) {
        clearConsole();
      }

      if (env.raw.FAST_REFRESH && semver.lt(react.version, '16.10.0')) {
        console.log(
          chalk.yellow(
            `Fast Refresh requires React 16.10 or higher. You are using React ${react.version}.`
          )
        );
      }

      console.log(chalk.cyan('Starting the development server...\n'));
      openBrowser(urls.localUrlForBrowser);
    });

    ['SIGINT', 'SIGTERM'].forEach(function (sig) {
      process.on(sig, function () {
        devServer.close();
        process.exit();
      });
    });

    if (process.env.CI !== 'true') {
      // Gracefully exit when stdin ends
      process.stdin.on('end', function () {
        devServer.close();
        process.exit();
      });
    }
  })

  // 如果操作过程中有报错退出进程
  .catch(err => {
    if (err && err.message) {
      console.log(err.message);
    }
    process.exit(1);
  });

// Source maps are resource heavy and can cause out of memory issue for large source files.
// 是否会生成sourceMap文件 
// 安装 cross-env 在package.json scripts指定命令中添加 GENERATE_SOURCEMAP=false
const shouldUseSourceMap = process.env.GENERATE_SOURCEMAP !== 'false';

const webpackDevClientEntry = require.resolve(
  'react-dev-utils/webpackHotDevClient'
);
const reactRefreshOverlayEntry = require.resolve(
  'react-dev-utils/refreshOverlayInterop'
);

// Some apps do not need the benefits of saving a web request, so not inlining the chunk
// makes for a smoother build process.
// 是否需要吧runtime文件内联在打包的js中
const shouldInlineRuntimeChunk = process.env.INLINE_RUNTIME_CHUNK !== 'false';

const emitErrorsAsWarnings = process.env.ESLINT_NO_DEV_ERRORS === 'true';
const disableESLintPlugin = process.env.DISABLE_ESLINT_PLUGIN === 'true';

// 最小转换成base64图片的大小
const imageInlineSizeLimit = parseInt(
  process.env.IMAGE_INLINE_SIZE_LIMIT || '10000'
);

// Check if TypeScript is setup
const useTypeScript = fs.existsSync(paths.appTsConfig);

// Get the path to the uncompiled service worker (if it exists).
const swSrc = paths.swSrc;

// style files regexes
const cssRegex = /\.css$/;
const cssModuleRegex = /\.module\.css$/;
const sassRegex = /\.(scss|sass)$/;
const sassModuleRegex = /\.module\.(scss|sass)$/;

const hasJsxRuntime = (() => {
  if (process.env.DISABLE_NEW_JSX_TRANSFORM === 'true') {
    return false;
  }

  try {
    require.resolve('react/jsx-runtime');
    return true;
  } catch (e) {
    return false;
  }
})();

// This is the production and development configuration.
// It is focused on developer experience, fast rebuilds, and a minimal bundle.
// 最终返回的开发或生产环境的函数
module.exports = function (webpackEnv) {
  const isEnvDevelopment = webpackEnv === 'development';
  const isEnvProduction = webpackEnv === 'production';

  // Variable used for enabling profiling in Production
  // passed into alias object. Uses a flag if passed into the build command
  const isEnvProductionProfile =
    isEnvProduction && process.argv.includes('--profile');

  // We will provide `paths.publicUrlOrPath` to our app
  // as %PUBLIC_URL% in `index.html` and `process.env.PUBLIC_URL` in JavaScript.
  // Omit trailing slash as %PUBLIC_URL%/xyz looks better than %PUBLIC_URL%xyz.
  // Get environment variables to inject into our app.

  // 获取环境变量的方法 必须以 REACT_APP开头
  const env = getClientEnvironment(paths.publicUrlOrPath.slice(0, -1));

  const shouldUseReactRefresh = env.raw.FAST_REFRESH;

  // common function to get style loaders
  // 获取处理样式文件的loader
  const getStyleLoaders = (cssOptions, preProcessor) => {
    const loaders = [
      // 开发环境用style-loader 生产环境压缩css
      isEnvDevelopment && require.resolve('style-loader'),
      isEnvProduction && {
        loader: MiniCssExtractPlugin.loader,
        // css is located in `static/css`, use '../../' to locate index.html folder
        // in production `paths.publicUrlOrPath` can be a relative path
        options: paths.publicUrlOrPath.startsWith('.')
          ? { publicPath: '../../' }
          : {},
      },
      // 将样式整合到js中
      {
        loader: require.resolve('css-loader'),
        options: cssOptions,
      },
      {
        // Options for PostCSS as we reference these options twice
        // Adds vendor prefixing based on your specified browser support in
        // package.json
        // 做css兼容性处理
        loader: require.resolve('postcss-loader'),
        options: {
          // Necessary for external CSS imports to work
          // https://github.com/facebook/create-react-app/issues/2677
          ident: 'postcss',
          plugins: () => [
            require('postcss-flexbugs-fixes'),
            require('postcss-preset-env')({
              autoprefixer: {
                flexbox: 'no-2009',
              },
              stage: 3,
            }),
            // Adds PostCSS Normalize as the reset css with default options,
            // so that it honors browserslist config in package.json
            // which in turn let's users customize the target behavior as per their needs.
            postcssNormalize(),
          ],
          sourceMap: isEnvProduction ? shouldUseSourceMap : isEnvDevelopment,
        },
      },
    ].filter(Boolean);
    if (preProcessor) {
      loaders.push(
        {
          loader: require.resolve('resolve-url-loader'),
          options: {
            sourceMap: isEnvProduction ? shouldUseSourceMap : isEnvDevelopment,
            root: paths.appSrc,
          },
        },
        {
          loader: require.resolve(preProcessor),
          options: {
            sourceMap: true,
          },
        }
      );
    }
    return loaders;
  };

  return {
    mode: isEnvProduction ? 'production' : isEnvDevelopment && 'development',
    // Stop compilation early in production
    // 开发环境出错会继续打包，因为接下来代码可能被修改
    // 生产环境则立即停止打包
    bail: isEnvProduction,
    devtool: isEnvProduction
      ? shouldUseSourceMap
        ? 'source-map' // 生产环境
        : false
      : isEnvDevelopment && 'cheap-module-source-map', // 开发环境
    // These are the "entry points" to our application.
    // This means they will be the "root" imports that are included in JS bundle.
    entry:
      isEnvDevelopment && !shouldUseReactRefresh
        ? [
            // Include an alternative client for WebpackDevServer. A client's job is to
            // connect to WebpackDevServer by a socket and get notified about changes.
            // When you save a file, the client will either apply hot updates (in case
            // of CSS changes), or refresh the page (in case of JS changes). When you
            // make a syntax error, this client will display a syntax error overlay.
            // Note: instead of the default WebpackDevServer client, we use a custom one
            // to bring better experience for Create React App users. You can replace
            // the line below with these two lines if you prefer the stock client:
            //
            // require.resolve('webpack-dev-server/client') + '?/',
            // require.resolve('webpack/hot/dev-server'),
            //
            // When using the experimental react-refresh integration,
            // the webpack plugin takes care of injecting the dev client for us.
            webpackDevClientEntry,
            // Finally, this is your app's code:
            paths.appIndexJs,
            // We include the app code last so that if there is a runtime error during
            // initialization, it doesn't blow up the WebpackDevServer client, and
            // changing JS code would still trigger a refresh.
          ]
        : paths.appIndexJs,
    output: {
      // The build folder.
      // 生产环境输出到目录，开发环境不输出
      path: isEnvProduction ? paths.appBuild : undefined,
      // Add /* filename */ comments to generated require()s in the output.
      pathinfo: isEnvDevelopment,
      // There will be one main bundle, and one file per asynchronous chunk.
      // In development, it does not produce real files.
      filename: isEnvProduction
        ? 'static/js/[name].[contenthash:8].js'
        : isEnvDevelopment && 'static/js/bundle.js',
      // TODO: remove this when upgrading to webpack 5
      futureEmitAssets: true,
      // There are also additional JS chunk files if you use code splitting.
      // 经过代码分割的文件会带上chunk的后缀，用于区分入口文件
      chunkFilename: isEnvProduction
        ? 'static/js/[name].[contenthash:8].chunk.js'
        : isEnvDevelopment && 'static/js/[name].chunk.js',
      // webpack uses `publicPath` to determine where the app is being served from.
      // It requires a trailing slash, or the file assets will get an incorrect path.
      // We inferred the "public path" (such as / or /my-project) from homepage.
      publicPath: paths.publicUrlOrPath,
      // Point sourcemap entries to original disk location (format as URL on Windows)
      devtoolModuleFilenameTemplate: isEnvProduction
        ? info =>
            path
              .relative(paths.appSrc, info.absoluteResourcePath)
              .replace(/\\/g, '/')
        : isEnvDevelopment &&
          (info => path.resolve(info.absoluteResourcePath).replace(/\\/g, '/')),
      // Prevents conflicts when multiple webpack runtimes (from different apps)
      // are used on the same page.
      jsonpFunction: `webpackJsonp${appPackageJson.name}`,
      // this defaults to 'window', but by setting it to 'this' then
      // module chunks which are built will work in web workers as well.
      // 用this来统一顶级变量
      globalObject: 'this',
    },
    optimization: {
      minimize: isEnvProduction,
      minimizer: [
        // This is only used in production mode
        // 压缩 JS
        new TerserPlugin({
          terserOptions: {
            parse: {
              // We want terser to parse ecma 8 code. However, we don't want it
              // to apply any minification steps that turns valid ecma 5 code
              // into invalid ecma 5 code. This is why the 'compress' and 'output'
              // sections only apply transformations that are ecma 5 safe
              // https://github.com/facebook/create-react-app/pull/4234
              ecma: 8,
            },
            compress: {
              ecma: 5,
              warnings: false,
              // Disabled because of an issue with Uglify breaking seemingly valid code:
              // https://github.com/facebook/create-react-app/issues/2376
              // Pending further investigation:
              // https://github.com/mishoo/UglifyJS2/issues/2011
              comparisons: false,
              // Disabled because of an issue with Terser breaking valid code:
              // https://github.com/facebook/create-react-app/issues/5250
              // Pending further investigation:
              // https://github.com/terser-js/terser/issues/120
              inline: 2,
            },
            mangle: {
              safari10: true,
            },
            // Added for profiling in devtools
            keep_classnames: isEnvProductionProfile,
            keep_fnames: isEnvProductionProfile,
            output: {
              ecma: 5,
              comments: false,
              // Turned on because emoji and regex is not minified properly using default
              // https://github.com/facebook/create-react-app/issues/2488
              ascii_only: true,
            },
          },
          sourceMap: shouldUseSourceMap,
        }),
        // This is only used in production mode
        // 压缩CSS
        new OptimizeCSSAssetsPlugin({
          cssProcessorOptions: {
            parser: safePostCssParser,
            map: shouldUseSourceMap
              ? {
                  // `inline: false` forces the sourcemap to be output into a
                  // separate file
                  inline: false,
                  // `annotation: true` appends the sourceMappingURL to the end of
                  // the css file, helping the browser find the sourcemap
                  annotation: true,
                }
              : false,
          },
          cssProcessorPluginOptions: {
            preset: ['default', { minifyFontValues: { removeQuotes: false } }],
          },
        }),
      ],
      // Automatically split vendor and commons
      // https://twitter.com/wSokra/status/969633336732905474
      // https://medium.com/webpack/webpack-4-code-splitting-chunk-graph-and-the-splitchunks-optimization-be739a861366
      // 使用的默认配置
      splitChunks: {
        chunks: 'all',
        name: isEnvDevelopment,
      },
      // Keep the runtime chunk separated to enable long term caching
      // https://twitter.com/wSokra/status/969679223278505985
      // https://github.com/facebook/create-react-app/issues/5358
      // 分别打包runtime文件
      runtimeChunk: {
        name: entrypoint => `runtime-${entrypoint.name}`,
      },
    },
    resolve: {
      // This allows you to set a fallback for where webpack should look for modules.
      // We placed these paths second because we want `node_modules` to "win"
      // if there are any conflicts. This matches Node resolution mechanism.
      // https://github.com/facebook/create-react-app/issues/253
      // 依赖模块查找路径
      modules: ['node_modules', paths.appNodeModules].concat(
        modules.additionalModulePaths || []
      ),
      // These are the reasonable defaults supported by the Node ecosystem.
      // We also include JSX as a common component filename extension to support
      // some tools, although we do not recommend using it, see:
      // https://github.com/facebook/create-react-app/issues/290
      // `web` extension prefixes have been added for better support
      // for React Native Web.
      extensions: paths.moduleFileExtensions
        .map(ext => `.${ext}`)
        .filter(ext => useTypeScript || !ext.includes('ts')),
      // 定义一些别名
      alias: {
        // Support React Native Web
        // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
        'react-native': 'react-native-web',
        // Allows for better profiling with ReactDevTools
        ...(isEnvProductionProfile && {
          'react-dom$': 'react-dom/profiling',
          'scheduler/tracing': 'scheduler/tracing-profiling',
        }),
        ...(modules.webpackAliases || {}),
      },
      plugins: [
        // Adds support for installing with Plug'n'Play, leading to faster installs and adding
        // guards against forgotten dependencies and such.
        PnpWebpackPlugin,
        // Prevents users from importing files from outside of src/ (or node_modules/).
        // This often causes confusion because we only process files within src/ with babel.
        // To fix this, we prevent you from importing files out of src/ -- if you'd like to,
        // please link the files into your node_modules/ and let module-resolution kick in.
        // Make sure your source files are compiled, as they will not be processed in any way.
        // 用于检测查找文件的范围，必须在src下面或者package.json文件
        new ModuleScopePlugin(paths.appSrc, [
          paths.appPackageJson,
          reactRefreshOverlayEntry,
        ]),
      ],
    },
    resolveLoader: {
      plugins: [
        // Also related to Plug'n'Play, but this time it tells webpack to load its loaders
        // from the current package.
        PnpWebpackPlugin.moduleLoader(module),
      ],
    },
    module: {
      strictExportPresence: true,
      rules: [
        // Disable require.ensure as it's not a standard language feature.
        // requireEnsure不在被支持
        { parser: { requireEnsure: false } },
        {
          // "oneOf" will traverse all following loaders until one will
          // match the requirements. When no loader matches it will fall
          // back to the "file" loader at the end of the loader list.
          // 用于优化解析一个匹配将不在检查
          oneOf: [
            // TODO: Merge this config once `image/avif` is in the mime-db
            // https://github.com/jshttp/mime-db
            {
              test: [/\.avif$/],
              loader: require.resolve('url-loader'),
              options: {
                limit: imageInlineSizeLimit,
                mimetype: 'image/avif',
                name: 'static/media/[name].[hash:8].[ext]',
              },
            },
            // "url" loader works like "file" loader except that it embeds assets
            // smaller than specified limit in bytes as data URLs to avoid requests.
            // A missing `test` is equivalent to a match.
            // 
            {
              test: [/\.bmp$/, /\.gif$/, /\.jpe?g$/, /\.png$/],
              loader: require.resolve('url-loader'),
              options: {
                limit: imageInlineSizeLimit,
                name: 'static/media/[name].[hash:8].[ext]',
              },
            },
            // Process application JS with Babel.
            // The preset includes JSX, Flow, TypeScript, and some ESnext features.
            {
              test: /\.(js|mjs|jsx|ts|tsx)$/,
              // 只处理src文件夹目录下面的文件
              include: paths.appSrc,
              // babel-loader的配置在package.json中添加
              loader: require.resolve('babel-loader'),
              options: {
                customize: require.resolve(
                  'babel-preset-react-app/webpack-overrides'
                ),
                presets: [
                  [
                    require.resolve('babel-preset-react-app'),
                    {
                      runtime: hasJsxRuntime ? 'automatic' : 'classic',
                    },
                  ],
                ],
                
                plugins: [
                  [
                    require.resolve('babel-plugin-named-asset-import'),
                    {
                      loaderMap: {
                        svg: {
                          ReactComponent:
                            '@svgr/webpack?-svgo,+titleProp,+ref![path]',
                        },
                      },
                    },
                  ],
                  isEnvDevelopment &&
                    shouldUseReactRefresh &&
                    require.resolve('react-refresh/babel'),
                ].filter(Boolean),
                // This is a feature of `babel-loader` for webpack (not Babel itself).
                // It enables caching results in ./node_modules/.cache/babel-loader/
                // directory for faster rebuilds.
                cacheDirectory: true,
                // See #6846 for context on why cacheCompression is disabled
                cacheCompression: false,
                compact: isEnvProduction,
              },
            },
            // Process any JS outside of the app with Babel.
            // Unlike the application JS, we only compile the standard ES features.
            // 除了src文件下面以外的js文件
            {
              test: /\.(js|mjs)$/,
              exclude: /@babel(?:\/|\\{1,2})runtime/,
              loader: require.resolve('babel-loader'),
              options: {
                babelrc: false,
                configFile: false,
                compact: false,
                presets: [
                  [
                    require.resolve('babel-preset-react-app/dependencies'),
                    { helpers: true },
                  ],
                ],
                cacheDirectory: true,
                // See #6846 for context on why cacheCompression is disabled
                cacheCompression: false,
                
                // Babel sourcemaps are needed for debugging into node_modules
                // code.  Without the options below, debuggers like VSCode
                // show incorrect code and set breakpoints on the wrong lines.
                sourceMaps: shouldUseSourceMap,
                inputSourceMap: shouldUseSourceMap,
              },
            },
            // "postcss" loader applies autoprefixer to our CSS.
            // "css" loader resolves paths in CSS and adds assets as dependencies.
            // "style" loader turns CSS into JS modules that inject <style> tags.
            // In production, we use MiniCSSExtractPlugin to extract that CSS
            // to a file, but in development "style" loader enables hot editing
            // of CSS.
            // By default we support CSS Modules with the extension .module.css
            {
              test: cssRegex,
              exclude: cssModuleRegex,
              use: getStyleLoaders({
                importLoaders: 1,
                sourceMap: isEnvProduction
                  ? shouldUseSourceMap
                  : isEnvDevelopment,
              }),
              // Don't consider CSS imports dead code even if the
              // containing package claims to have no side effects.
              // Remove this when webpack adds a warning or an error for this.
              // See https://github.com/webpack/webpack/issues/6571
              // 样式资源是有副作用的，不要进行treeShaking
              sideEffects: true,
            },
            // Adds support for CSS Modules (https://github.com/css-modules/css-modules)
            // using the extension .module.css
            // 处理模块化样式， 文件以module.css结尾
            {
              test: cssModuleRegex,
              use: getStyleLoaders({
                importLoaders: 1,
                sourceMap: isEnvProduction
                  ? shouldUseSourceMap
                  : isEnvDevelopment,
                modules: {
                  getLocalIdent: getCSSModuleLocalIdent,
                },
              }),
            },
            // Opt-in support for SASS (using .scss or .sass extensions).
            // By default we support SASS Modules with the
            // extensions .module.scss or .module.sass
            // 处理sassloader
            {
              test: sassRegex,
              exclude: sassModuleRegex,
              use: getStyleLoaders(
                {
                  importLoaders: 3,
                  sourceMap: isEnvProduction
                    ? shouldUseSourceMap
                    : isEnvDevelopment,
                },
                'sass-loader'
              ),
              // Don't consider CSS imports dead code even if the
              // containing package claims to have no side effects.
              // Remove this when webpack adds a warning or an error for this.
              // See https://github.com/webpack/webpack/issues/6571
              sideEffects: true,
            },
            // Adds support for CSS Modules, but using SASS
            // using the extension .module.scss or .module.sass
            {
              test: sassModuleRegex,
              use: getStyleLoaders(
                {
                  importLoaders: 3,
                  sourceMap: isEnvProduction
                    ? shouldUseSourceMap
                    : isEnvDevelopment,
                  modules: {
                    getLocalIdent: getCSSModuleLocalIdent,
                  },
                },
                'sass-loader'
              ),
            },
            // "file" loader makes sure those assets get served by WebpackDevServer.
            // When you `import` an asset, you get its (virtual) filename.
            // In production, they would get copied to the `build` folder.
            // This loader doesn't use a "test" so it will catch all modules
            // that fall through the other loaders.
            // 一些特殊文件，视频文件等，直接输出
            {
              loader: require.resolve('file-loader'),
              // Exclude `js` files to keep "css" loader working as it injects
              // its runtime that would otherwise be processed through "file" loader.
              // Also exclude `html` and `json` extensions so they get processed
              // by webpacks internal loaders.
              exclude: [/\.(js|mjs|jsx|ts|tsx)$/, /\.html$/, /\.json$/],
              options: {
                name: 'static/media/[name].[hash:8].[ext]',
              },
            },
            // ** STOP ** Are you adding a new loader?
            // Make sure to add the new loader(s) before the "file" loader.
          ],
        },
      ],
    },
    plugins: [
      // Generates an `index.html` file with the <script> injected.
      new HtmlWebpackPlugin(
        Object.assign(
          {},
          {
            inject: true,
            template: paths.appHtml,
          },
          // 生产环境加了压缩的配置
          isEnvProduction
            ? {
                minify: {
                  removeComments: true,
                  collapseWhitespace: true,
                  removeRedundantAttributes: true,
                  useShortDoctype: true,
                  removeEmptyAttributes: true,
                  removeStyleLinkTypeAttributes: true,
                  keepClosingSlash: true,
                  minifyJS: true,
                  minifyCSS: true,
                  minifyURLs: true,
                },
              }
            : undefined
        )
      ),
      // Inlines the webpack runtime script. This script is too small to warrant
      // a network request.
      // https://github.com/facebook/create-react-app/issues/5358
      // 是否要内联runtime文件
      isEnvProduction &&
        shouldInlineRuntimeChunk &&
        new InlineChunkHtmlPlugin(HtmlWebpackPlugin, [/runtime-.+[.]js/]),
      // Makes some environment variables available in index.html.
      // The public URL is available as %PUBLIC_URL% in index.html, e.g.:
      // <link rel="icon" href="%PUBLIC_URL%/favicon.ico">
      // It will be an empty string unless you specify "homepage"
      // in `package.json`, in which case it will be the pathname of that URL.
      // 解析html中的 %PUBLIC_URL%
      new InterpolateHtmlPlugin(HtmlWebpackPlugin, env.raw),
      // This gives some necessary context to module not found errors, such as
      // the requesting resource.
      // 给没有找到的模块提供更好的提示
      new ModuleNotFoundPlugin(paths.appPath),
      // Makes some environment variables available to the JS code, for example:
      // if (process.env.NODE_ENV === 'production') { ... }. See `./env.js`.
      // It is absolutely essential that NODE_ENV is set to production
      // during a production build.
      // Otherwise React will be compiled in the very slow development mode.
      // 定义环境变量
      new webpack.DefinePlugin(env.stringified),
      // This is necessary to emit hot updates (CSS and Fast Refresh):
      // 开发环境提供热模块替换
      isEnvDevelopment && new webpack.HotModuleReplacementPlugin(),
      // Experimental hot reloading for React .
      // https://github.com/facebook/react/tree/master/packages/react-refresh

      isEnvDevelopment &&
        shouldUseReactRefresh &&
        new ReactRefreshWebpackPlugin({
          overlay: {
            entry: webpackDevClientEntry,
            // The expected exports are slightly different from what the overlay exports,
            // so an interop is included here to enable feedback on module-level errors.
            module: reactRefreshOverlayEntry,
            // Since we ship a custom dev client and overlay integration,
            // the bundled socket handling logic can be eliminated.
            sockIntegration: false,
          },
        }),
      // Watcher doesn't work well if you mistype casing in a path so we use
      // a plugin that prints an error when you attempt to do this.
      // See https://github.com/facebook/create-react-app/issues/240
      // 文件路径严格区分大小写
      isEnvDevelopment && new CaseSensitivePathsPlugin(),
      // If you require a missing module and then `npm install` it, you still have
      // to restart the development server for webpack to discover it. This plugin
      // makes the discovery automatic so you don't have to restart.
      // See https://github.com/facebook/create-react-app/issues/186
      // 监视nodemodules一旦变化会重启server
      isEnvDevelopment &&
        new WatchMissingNodeModulesPlugin(paths.appNodeModules),
      // 提取css为单独的文件
      isEnvProduction &&
        new MiniCssExtractPlugin({
          // Options similar to the same options in webpackOptions.output
          // both options are optional
          filename: 'static/css/[name].[contenthash:8].css',
          chunkFilename: 'static/css/[name].[contenthash:8].chunk.css',
        }),
      // Generate an asset manifest file with the following content:
      // - "files" key: Mapping of all asset filenames to their corresponding
      //   output file so that tools can pick it up without having to parse
      //   `index.html`
      // - "entrypoints" key: Array of files which are included in `index.html`,
      //   can be used to reconstruct the HTML if necessary
      new ManifestPlugin({
        fileName: 'asset-manifest.json',
        publicPath: paths.publicUrlOrPath,
        generate: (seed, files, entrypoints) => {
          const manifestFiles = files.reduce((manifest, file) => {
            manifest[file.name] = file.path;
            return manifest;
          }, seed);
          const entrypointFiles = entrypoints.main.filter(
            fileName => !fileName.endsWith('.map')
          );

          return {
            files: manifestFiles,
            entrypoints: entrypointFiles,
          };
        },
      }),
      // Moment.js is an extremely popular library that bundles large locale files
      // by default due to how webpack interprets its code. This is a practical
      // solution that requires the user to opt into importing specific locales.
      // https://github.com/jmblog/how-to-optimize-momentjs-with-webpack
      // You can remove this if you don't use Moment.js:
      // 优化momentjs
      new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
      // Generate a service worker script that will precache, and keep up to date,
      // the HTML & assets that are part of the webpack build.
      isEnvProduction &&
        fs.existsSync(swSrc) &&
        new WorkboxWebpackPlugin.InjectManifest({
          swSrc,
          dontCacheBustURLsMatching: /\.[0-9a-f]{8}\./,
          exclude: [/\.map$/, /asset-manifest\.json$/, /LICENSE/],
          // Bump up the default maximum size (2mb) that's precached,
          // to make lazy-loading failure scenarios less likely.
          // See https://github.com/cra-template/pwa/issues/13#issuecomment-722667270
          maximumFileSizeToCacheInBytes: 5 * 1024 * 1024,
        }),
      // TypeScript type checking
      useTypeScript &&
        new ForkTsCheckerWebpackPlugin({
          typescript: resolve.sync('typescript', {
            basedir: paths.appNodeModules,
          }),
          async: isEnvDevelopment,
          checkSyntacticErrors: true,
          resolveModuleNameModule: process.versions.pnp
            ? `${__dirname}/pnpTs.js`
            : undefined,
          resolveTypeReferenceDirectiveModule: process.versions.pnp
            ? `${__dirname}/pnpTs.js`
            : undefined,
          tsconfig: paths.appTsConfig,
          reportFiles: [
            // This one is specifically to match during CI tests,
            // as micromatch doesn't match
            // '../cra-template-typescript/template/src/App.tsx'
            // otherwise.
            '../**/src/**/*.{ts,tsx}',
            '**/src/**/*.{ts,tsx}',
            '!**/src/**/__tests__/**',
            '!**/src/**/?(*.)(spec|test).*',
            '!**/src/setupProxy.*',
            '!**/src/setupTests.*',
          ],
          silent: true,
          // The formatter is invoked directly in WebpackDevServerUtils during development
          formatter: isEnvProduction ? typescriptFormatter : undefined,
        }),
      !disableESLintPlugin &&
        new ESLintPlugin({
          // Plugin options
          extensions: ['js', 'mjs', 'jsx', 'ts', 'tsx'],
          formatter: require.resolve('react-dev-utils/eslintFormatter'),
          eslintPath: require.resolve('eslint'),
          failOnError: !(isEnvDevelopment && emitErrorsAsWarnings),
          context: paths.appSrc,
          cache: true,
          cacheLocation: path.resolve(
            paths.appNodeModules,
            '.cache/.eslintcache'
          ),
          // ESLint class options
          cwd: paths.appPath,
          resolvePluginsRelativeTo: __dirname,
          baseConfig: {
            extends: [require.resolve('eslint-config-react-app/base')],
            rules: {
              ...(!hasJsxRuntime && {
                'react/react-in-jsx-scope': 'error',
              }),
            },
          },
        }),
    ].filter(Boolean),
    // Some libraries import Node modules but don't use them in the browser.
    // Tell webpack to provide empty mocks for them so importing them works.
    // 避免打包一些node模块文件
    node: {
      module: 'empty',
      dgram: 'empty',
      dns: 'mock',
      fs: 'empty',
      http2: 'empty',
      net: 'empty',
      tls: 'empty',
      child_process: 'empty',
    },
    // Turn off performance processing because we utilize
    // our own hints via the FileSizeReporter
    // 关闭性能分析
    performance: false,
  };
};

const measureFileSizesBeforeBuild =
  FileSizeReporter.measureFileSizesBeforeBuild;
const printFileSizesAfterBuild = FileSizeReporter.printFileSizesAfterBuild;
const useYarn = fs.existsSync(paths.yarnLockFile);

// These sizes are pretty large. We'll warn for bundles exceeding them.
const WARN_AFTER_BUNDLE_GZIP_SIZE = 512 * 1024;
const WARN_AFTER_CHUNK_GZIP_SIZE = 1024 * 1024;

const isInteractive = process.stdout.isTTY;

// Warn and crash if required files are missing
if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
  process.exit(1);
}

const argv = process.argv.slice(2);
const writeStatsJson = argv.indexOf('--stats') !== -1;

// Generate configuration
const config = configFactory('production');

// We require that you explicitly set browsers and do not fall back to
// browserslist defaults.
const { checkBrowsers } = require('react-dev-utils/browsersHelper');
checkBrowsers(paths.appPath, isInteractive)
  .then(() => {
    // First, read the current file sizes in build directory.
    // This lets us display how much they changed later.
    return measureFileSizesBeforeBuild(paths.appBuild);
  })
  .then(previousFileSizes => {
    // Remove all content but keep the directory so that
    // if you're in it, you don't end up in Trash
    fs.emptyDirSync(paths.appBuild);
    // Merge with the public folder
    copyPublicFolder();
    // Start the webpack build
    return build(previousFileSizes);
  })
  .then(
    ({ stats, previousFileSizes, warnings }) => {
      if (warnings.length) {
        console.log(chalk.yellow('Compiled with warnings.\n'));
        console.log(warnings.join('\n\n'));
        console.log(
          '\nSearch for the ' +
            chalk.underline(chalk.yellow('keywords')) +
            ' to learn more about each warning.'
        );
        console.log(
          'To ignore, add ' +
            chalk.cyan('// eslint-disable-next-line') +
            ' to the line before.\n'
        );
      } else {
        console.log(chalk.green('Compiled successfully.\n'));
      }

      console.log('File sizes after gzip:\n');
      printFileSizesAfterBuild(
        stats,
        previousFileSizes,
        paths.appBuild,
        WARN_AFTER_BUNDLE_GZIP_SIZE,
        WARN_AFTER_CHUNK_GZIP_SIZE
      );
      console.log();

      const appPackage = require(paths.appPackageJson);
      const publicUrl = paths.publicUrlOrPath;
      const publicPath = config.output.publicPath;
      const buildFolder = path.relative(process.cwd(), paths.appBuild);
      printHostingInstructions(
        appPackage,
        publicUrl,
        publicPath,
        buildFolder,
        useYarn
      );
    },
    err => {
      const tscCompileOnError = process.env.TSC_COMPILE_ON_ERROR === 'true';
      if (tscCompileOnError) {
        console.log(
          chalk.yellow(
            'Compiled with the following type errors (you may want to check these before deploying your app):\n'
          )
        );
        printBuildError(err);
      } else {
        console.log(chalk.red('Failed to compile.\n'));
        printBuildError(err);
        process.exit(1);
      }
    }
  )
  .catch(err => {
    if (err && err.message) {
      console.log(err.message);
    }
    process.exit(1);
  });

// Create the production build and print the deployment instructions.
function build(previousFileSizes) {
  console.log('Creating an optimized production build...');

  const compiler = webpack(config);
  return new Promise((resolve, reject) => {
    compiler.run((err, stats) => {
      let messages;
      if (err) {
        if (!err.message) {
          return reject(err);
        }

        let errMessage = err.message;

        // Add additional information for postcss errors
        if (Object.prototype.hasOwnProperty.call(err, 'postcssNode')) {
          errMessage +=
            '\nCompileError: Begins at CSS selector ' +
            err['postcssNode'].selector;
        }

        messages = formatWebpackMessages({
          errors: [errMessage],
          warnings: [],
        });
      } else {
        messages = formatWebpackMessages(
          stats.toJson({ all: false, warnings: true, errors: true })
        );
      }
      if (messages.errors.length) {
        // Only keep the first error. Others are often indicative
        // of the same problem, but confuse the reader with noise.
        if (messages.errors.length > 1) {
          messages.errors.length = 1;
        }
        return reject(new Error(messages.errors.join('\n\n')));
      }
      if (
        process.env.CI &&
        (typeof process.env.CI !== 'string' ||
          process.env.CI.toLowerCase() !== 'false') &&
        messages.warnings.length
      ) {
        console.log(
          chalk.yellow(
            '\nTreating warnings as errors because process.env.CI = true.\n' +
              'Most CI servers set it automatically.\n'
          )
        );
        return reject(new Error(messages.warnings.join('\n\n')));
      }

      const resolveArgs = {
        stats,
        previousFileSizes,
        warnings: messages.warnings,
      };

      if (writeStatsJson) {
        return bfj
          .write(paths.appBuild + '/bundle-stats.json', stats.toJson())
          .then(() => resolve(resolveArgs))
          .catch(error => reject(new Error(error)));
      }

      return resolve(resolveArgs);
    });
  });
}

function copyPublicFolder() {
  fs.copySync(paths.appPublic, paths.appBuild, {
    dereference: true,
    filter: file => file !== paths.appHtml,
  });
}

let i = 0, j = 1;

const next = [0]

for(;j < pattern.length;j++){

}

while(i>0 &&　pattern[i]！==pattern[j]) {
  i = next[i-1]
}

let i=0;j=1;
const next = [0];
for(;j < pattern.length;j++){
  while(i>0 &&　pattern[i]！==pattern[j]) {
    i = next[i-1]
  }
  if(pattern[i]===pattern[j]) i++
  next[j]=i;
}

let m=0;
let n=0;

for(;m<sourceString.length;m++){
  if (sourceString[m] === pattern[n]) n++
}

while(n>0 && sourceString[m] === pattern[n]) n = next[n-1]

let m = 0;
let n = 0;
for(;m<sourceString.length;m++) {
  while (n > 0 && sourceString[m] !== pattern[n]) {
    n = next[n - 1];
  }
  if (sourceString[m] === pattern[n]) n++
  if (n === pattern.length) return m - n + 1;
}
return -1;

const kmp = (haystack, needle) => {
  if (needle.length == 0) return 0;
  const next = [0];
  for (let i = 0, j = 1; j < needle.length; j++) {
    while (i && needle[j] !== needle[i]) {
      i = next[i - 1];
    }
    if (needle[j] === needle[i]) i++;
    next[j] = i;
  }
  let m = 0;
  let n = 0;
  for(;m<sourceString.length;m++) {
    while (n > 0 && haystack[m] !== needle[n]) {
      n = next[n - 1];
    }
    if (haystack[m] === needle[n]) n++
    if (n === needle.length) return m - n + 1;
  }
  return -1;
}

import {atom, selector, useRecoilState} from 'recoil';

const tempFahrenheit = atom({
  key: 'tempFahrenheit',
  default: 32,
});

const tempCelcius = selector({
  key: 'tempCelcius',
  get: ({get}) => ((get(tempFahrenheit) - 32) * 5) / 9,
  set: ({set}, newValue) => set(tempFahrenheit, (newValue * 9) / 5 + 32),
});

useTransactionObservation(({atomValues,modifiedAtoms,...} => {}))

const counter = atom({
  key: 'myCounter',
  default: 0,
  validator: (untrustedInput),
  metadata: ...
})