create-react-app 源码学习

前言

最近想写一些东西，学习学习全栈开发，就从熟悉的react开始，一直开发模式都是组件形式，对 create-react-app源码不了解，须要从新学习下！
网上找了不少资料，刷官网...
找到一个写的很全面的，可是 create-react-app 已更新版本，我下载的是v3.3.0版本，版本不同源码也会有些出入，因此这里也记录下本身的学习内容，方便后期自我查看和学习。

文中都是借鉴和一些自我理解，有些错误或者理解上的误差，欢迎指正。

原文连接：https://segmentfault.com/a/11...

create-react-app 源码**

• 版本: v3.3.0github
• githu下载地址: https://github.com/mintsweet/...

目录

├── .github --- 项目中提的issue和pr的规范
├── docusaurus--- facebook的开源的用于简化构建,部署,和维护的博客网站
├── packages --- 包 项目核心
├── tasks--- 任务
├── test--- 测试文件
├── .eslintignore --- eslint检查时忽略文件
├── .eslintrc.json --- eslint 配置文件
├── .gitignore --- git提交时忽略文件
├── .travis.yml --- travis配置文件
├── .yarnrc --- yarn配置文件
├── azure-pipelines-test-job.yml--- Azure Pipelines test配置
├── azure-pipelines.yml --- Azure Pipelines配置,用于在Linux，Windows和macOS上构建和测试create-react-app
├── CHANGELOG-0.x.md --- 版本变动说明文件
├── CHANGELOG-1.x.md --- 版本变动说明文件
├── CHANGELOG-2.x.md --- 版本变动说明文件
├── CHANGELOG.md --- 当前版本变动说明文件
├── CODE_OF_CONDUCT.md --- facebook 代码行为准则说明
├── CONTRIBUTING.md--- 项目的核心说明
├── lerna.json--- lerna 配置文件
├── LICENSE --- 开源协议
├── netlify.toml --- 能够理解为docusaurus的配置设置
├── package.json --- 项目配置文件
├── README.md --- 项目使用说明
├── screencast-error.svg
└── screencast.svg

packages 文件

├── babel-plugin-named-asset-import
├── babel-preset-react-app
├── confusing-browser-globals
├── cra-template
├── cra-template-typescript
├── create-react-app
├── eslint-config-react-app
├── react-app-polyfill
├── react-dev-utils
├── react-error-overlay
└── react-scripts

代码的入口在packages/create-react-app/index.js下，核心代码在createReactApp.js中

断点调试：配置 vscode 的 debug 文件

这里添加三种环境，是 create-react-app 的不一样种使用方式

• create-react-app study-create-react-app-source
• create-react-app
• create-react-app study-create-react-app-source-ts --typescript

VsCode中Debug调试插件配置

依赖包做用分析

包	包做用
validate-npm-package-name	判断给定的字符串是否是符合npm包名称的规范,检查包名是否合法 validate
chalk	给命令行输入的log设置颜色 chalk
commander	自定义shell命令的工具，也就是能够用它代管Node命令，具体使用能够查看commander
semver	用于版本比较的工具，好比哪一个版本大，版本命名是否合法等
envinfo	输出当前环境的信息,用于比较Node版本 envinfo
fs-extra	Node自带文件模块的外部扩展模块 fs-extra
cross-spawn	用来执行node进程,Node跨平台解决方案，解决在windows下各类问题,详细看 cross-spawn
hyperquest	用于将http请求流媒体传输,详细看 hyperquest
dns	用来检测是否可以请求到指定的地址 dns

index.js

'use strict';

var currentNodeVersion = process.versions.node; // 返回Node版本信息，若是有多个版本返回多个版本
var semver = currentNodeVersion.split('.'); // 全部Node版本的集合
var major = semver[0]; // 取出第一个Node版本信息

if (major < 8) {  // 校验当前node版本是否低于8
  console.error(
    'You are running Node ' +
      currentNodeVersion +
      '.\n' +
      'Create React App requires Node 8 or higher. \n' +
      'Please update your version of Node.'
  );
  process.exit(1);
}
require('./createReactApp');

index.js 的代码很是的简单，其实就是对 node 的版本作了一下校验，若是版本号低于 8,就退出应用程序，不然直接进入到核心文件中，createReactApp.js中

createReactApp.js

createReactApp 的功能也很是简单其实，大概流程：

• 命令初始化，好比自定义create-react-app --info的输出等
• 判断是否输入项目名称，若是有，则根据参数去跑安装，若是没有，给提示，而后退出程序
• 修改 package.json
• 拷贝react-script下的模板文件

let projectName;  //定义了一个用来存储项目名称的变量

const program = new commander.Command(packageJson.name)
  .version(packageJson.version) //create-react-app -v 时候输出的值 packageJson 来自上面 const packageJson = require('./package.json');
  .arguments('<project-directory>')//定义 project-directory ，必填项
  .usage(`${chalk.green('<project-directory>')} [options]`) //  使用`create-react-app`第一行打印的信息，也就是使用说明

  .action(name => {
    projectName = name; //获取用户的输入，存为 projectName
  })
  .option('--verbose', 'print additional logs') // option配置`create-react-app -[option]`的选项，相似 --help -V
  .option('--info', 'print environment debug info') // 打印本地相关开发环境，操做系统，`Node`版本等等
  .option( // 指定 react-scripts
    '--scripts-version <alternative-package>',
    'use a non-standard version of react-scripts'
  )
  .option(// 项目建立template
    '--template <path-to-template>',
    'specify a template for the created project'
  )
  .option('--use-npm') // 指定使用npm 默认使用yarn
  .option('--use-pnp') //指定使用 pnp
  // TODO: Remove this in next major release.
  .option( // 指定使用ts，不过这里也有备注下一个版本就删除这项
    '--typescript',
    '(this option will be removed in favour of templates in the next major release of create-react-app)'
  )
  .allowUnknownOption()
  .on('--help', () => {
  // on('option', cb) 语法，输入 create-react-app --help 自动执行后面的操做输出帮助
    console.log(`    Only ${chalk.green('<project-directory>')} is required.`);
    console.log();
    console.log(
      `    A custom ${chalk.cyan('--scripts-version')} can be one of:`
    );
    console.log(`      - a specific npm version: ${chalk.green('0.8.2')}`);
    console.log(`      - a specific npm tag: ${chalk.green('@next')}`);
    console.log(
      `      - a custom fork published on npm: ${chalk.green(
        'my-react-scripts'
      )}`
    );
    console.log(
      `      - a local path relative to the current working directory: ${chalk.green(
        'file:../my-react-scripts'
      )}`
    );
    console.log(
      `      - a .tgz archive: ${chalk.green(
        'https://mysite.com/my-react-scripts-0.8.2.tgz'
      )}`
    );
    console.log(
      `      - a .tar.gz archive: ${chalk.green(
        'https://mysite.com/my-react-scripts-0.8.2.tar.gz'
      )}`
    );
    console.log(
      `    It is not needed unless you specifically want to use a fork.`
    );
    console.log();
    console.log(`    A custom ${chalk.cyan('--template')} can be one of:`);
    console.log(
      `      - a custom fork published on npm: ${chalk.green(
        'cra-template-typescript'
      )}`
    );
    console.log(
      `      - a local path relative to the current working directory: ${chalk.green(
        'file:../my-custom-template'
      )}`
    );
    console.log(
      `      - a .tgz archive: ${chalk.green(
        'https://mysite.com/my-custom-template-0.8.2.tgz'
      )}`
    );
    console.log(
      `      - a .tar.gz archive: ${chalk.green(
        'https://mysite.com/my-custom-template-0.8.2.tar.gz'
      )}`
    );
    console.log();
    console.log(
      `    If you have any problems, do not hesitate to file an issue:`
    );
    console.log(
      `      ${chalk.cyan(
        'https://github.com/facebook/create-react-app/issues/new'
      )}`
    );
    console.log();
  })
  .parse(process.argv);// commander 文档传送门,解析正常的`node

// 判断当前环境信息，退出
if (program.info) {
  console.log(chalk.bold('\nEnvironment Info:'));
  console.log(
    `\n  current version of ${packageJson.name}: ${packageJson.version}`
  );
  console.log(`  running from ${__dirname}`);
  return envinfo
    .run(
      {
        System: ['OS', 'CPU'],
        Binaries: ['Node', 'npm', 'Yarn'],
        Browsers: ['Chrome', 'Edge', 'Internet Explorer', 'Firefox', 'Safari'],
        npmPackages: ['react', 'react-dom', 'react-scripts'],
        npmGlobalPackages: ['create-react-app'],
      },
      {
        duplicates: true,
        showNotFound: true,
      }
    )
    .then(console.log);
}

//判断 projectName 是否为 undefined，而后输出相关提示信息，退出~
if (typeof projectName === 'undefined') {
  //没有项目名称也没有--info 会抛出异常
  console.error('Please specify the project directory:');
  console.log(
    `  ${chalk.cyan(program.name())} ${chalk.green('<project-directory>')}`
  );
  console.log();
  console.log('For example:');
  console.log(`  ${chalk.cyan(program.name())} ${chalk.green('my-react-app')}`);
  console.log();
  console.log(
    `Run ${chalk.cyan(`${program.name()} --help`)} to see all options.`
  );
  process.exit(1);
}

create-react-app <my-project>中的项目名称赋予了projectName 变量，此处的做用就是看看用户有没有传这个<my-project>参数，若是没有就会报错，并显示一些帮助信息，这里用到了另一个外部依赖envinfo。

createApp

修改vscode 配置文件

{  
  "type": "node",  
  "request": "launch",  
  "name": "CreateReactAppTs",  
  "program": "${workspaceFolder}/packages/create-react-    app/index.js",  
  "args": \[  
  "study-create-react-app-source-ts",  
  "--typescript",  
  "--use-npm"  
   \]  
  }

commander的option选项，若是加了这个选项这个值就是true，不然就是false，也就是说这里若是加了--typescript和--use-npm，那这个参数就是true，这些也都是咱们在commander中定义的 options，在源码里面 createApp 中，传入的参数分别为：

• projectName ：项目名称
• program.verbose 是否输出额外信息
• program.scriptsVersion 传入的脚本版本
• program.useNpm  是否使用 npm ，默认使用yarn
• program.usePnp  是否使用 Pnp，默认使用yarn
• program.typescript  是否使用 ts
• hiddenProgram.internalTestingTemplate 给开发者用的调试模板路径

function createApp(
  name,
  verbose,
  version,
  template,
  useNpm,
  usePnp,
  useTypeScript
) {

  // 检测node版本
  const unsupportedNodeVersion = !semver.satisfies(process.version, '>=8.10.0');
  // 判断node版本，若是结合TS一块儿使用就须要8.10或者更高版本，具体的方法在semver.js
  
  if (unsupportedNodeVersion && useTypeScript) {
    console.error(
      chalk.red(
        `You are using Node ${process.version} with the TypeScript template. Node 8.10 or higher is required to use TypeScript.\n`
      )
    );

    process.exit(1);
  } else if (unsupportedNodeVersion) {
    console.log(
      chalk.yellow(
        `You are using Node ${process.version} so the project will be bootstrapped with an old unsupported version of tools.\n\n` +
          `Please update to Node 8.10 or higher for a better, fully supported experience.\n`
      )
    );
    // Fall back to latest supported react-scripts on Node 4
    version = 'react-scripts@0.9.x';
  }

  const root = path.resolve(name); //path 拼接路径
  const appName = path.basename(root); //获取文件名

  checkAppName(appName); //检查传入的文件名合法性
  fs.ensureDirSync(name); //确保目录存在，若是不存在则建立一个
  if (!isSafeToCreateProjectIn(root, name)) {//判断新建这个文件夹是否安全，不然直接退出
    process.exit(1);
  }
  console.log();

  // 到这里打印成功建立了一个`react`项目在指定目录下
  console.log(`Creating a new React app in ${chalk.green(root)}.`);
  console.log();
  
  // 定义package.json基础内容
  const packageJson = {
    name: appName,
    version: '0.1.0',
    private: true,
  };
  // 往咱们建立的文件夹中写入package.json文件
  fs.writeFileSync(
    path.join(root, 'package.json'),
    JSON.stringify(packageJson, null, 2) + os.EOL
  );

  // 定义常量 useYarn 若是传参有 --use-npm useYarn就是false，不然执行 shouldUseYarn() 检查yarn是否存在
  // 这一步就是以前说的他默认使用`yarn`，可是能够指定使用`npm`，若是指定使用了`npm`，`useYarn`就是`false`，否则执行 shouldUseYarn 函数
  // shouldUseYarn 用于检测本机是否安装了`yarn`
  const useYarn = useNpm ? false : shouldUseYarn();
  // 取得当前node进程的目录，提早获取保存下来，接下来这个值会被改变，若是后面须要用到这个值，后续其实取得值将不是这个
  // 因此这里的目的就是提早存好，省得我后续使用的时候很差去找，这个地方就是我执行初始化项目的目录，而不是初始化好的目录，是初始化的上级目录
  const originalDirectory = process.cwd();
  // 修改进程目录为底下子进程目录
  // 在这里就把进程目录修改成了咱们建立的目录
  process.chdir(root);
  // checkThatNpmCanReadCwd 这个函数的做用是检查进程目录是不是咱们建立的目录，也就是说若是进程不在咱们建立的目录里面，后续再执行`npm`安装的时候就会出错，因此提早检查
  if (!useYarn && !checkThatNpmCanReadCwd()) {
    process.exit(1);
  }

  if (!useYarn) { //关于 npm、pnp、yarn 的使用判断，版本校验等
    const npmInfo = checkNpmVersion();
    
    if (!npmInfo.hasMinNpm) {
      if (npmInfo.npmVersion) {
        console.log(
          chalk.yellow(
            `You are using npm ${npmInfo.npmVersion} so the project will be bootstrapped with an old unsupported version of tools.\n\n` +
              `Please update to npm 5 or higher for a better, fully supported experience.\n`
          )
        );
      }
      // Fall back to latest supported react-scripts for npm 3
      version = 'react-scripts@0.9.x';
    }
  } else if (usePnp) {
    const yarnInfo = checkYarnVersion();
    if (!yarnInfo.hasMinYarnPnp) {
      if (yarnInfo.yarnVersion) {
        console.log(
          chalk.yellow(
            `You are using Yarn ${yarnInfo.yarnVersion} together with the --use-pnp flag, but Plug'n'Play is only supported starting from the 1.12 release.\n\n` +
              `Please update to Yarn 1.12 or higher for a better, fully supported experience.\n`
          )
        );
      }
      // 1.11 had an issue with webpack-dev-middleware, so better not use PnP with it (never reached stable, but still)
      usePnp = false;
    }
  }

  if (useTypeScript) {
    console.log(
      chalk.yellow(
        'The --typescript option has been deprecated and will be removed in a future release.'
      )
    );
    console.log(
      chalk.yellow(
        `In future, please use ${chalk.cyan('--template typescript')}.`
      )
    );
    console.log();
    if (!template) {
      template = 'typescript';
    }
  }

  if (useYarn) {
    let yarnUsesDefaultRegistry = true;
    try {
      yarnUsesDefaultRegistry =
        execSync('yarnpkg config get registry')
          .toString()
          .trim() === 'https://registry.yarnpkg.com';
    } catch (e) {
      // ignore
    }
    if (yarnUsesDefaultRegistry) {
      fs.copySync(
        require.resolve('./yarn.lock.cached'),
        path.join(root, 'yarn.lock')
      );
    }
  }

  run(
    root,
    appName,
    version,
    verbose,
    originalDirectory,
    template,
    useYarn,
    usePnp
  );
}

代码很是简单，部分注释已经加载代码中，简单的说就是对一个本地环境的一些校验，版本检查、目录建立等，若是建立失败，则退出，若是版本较低，则使用对应低版本的create-react-app，最后调用 run 方法

• checkAppName()：用于检测文件名是否合法，
• isSafeToCreateProjectIn()：用于检测文件夹是否安全
• shouldUseYarn()：用于检测yarn在本机是否已经安装
• checkThatNpmCanReadCwd()：用于检测npm是否在正确的目录下执行
• checkNpmVersion()：用于检测npm在本机是否已经安装了

checkAppName

checkAPPName 方法主要的核心代码是validate-npm-package-namepackage，从名字便可看出，检查是否为合法的 npm 包名

function checkAppName(appName) {
  // 关于validateProjectName方法 在插件`validate-npm-package-name`index文件
  const validationResult = validateProjectName(appName);
  if (!validationResult.validForNewPackages) {
    console.error(
      chalk.red(
        `Cannot create a project named ${chalk.green(
          `"${appName}"`
        )} because of npm naming restrictions:\n`
      )
    );
    [
      ...(validationResult.errors || []),
      ...(validationResult.warnings || []),
    ].forEach(error => {
      console.error(chalk.red(`  * ${error}`));
    });
    console.error(chalk.red('\nPlease choose a different project name.'));
    process.exit(1);
  }

  // TODO: there should be a single place that holds the dependencies
  const dependencies = ['react', 'react-dom', 'react-scripts'].sort();
  if (dependencies.includes(appName)) {
    console.error(
      chalk.red(
        `Cannot create a project named ${chalk.green(
          `"${appName}"`
        )} because a dependency with the same name exists.\n` +
          `Due to the way npm works, the following names are not allowed:\n\n`
      ) +
        chalk.cyan(dependencies.map(depName => `  ${depName}`).join('\n')) +
        chalk.red('\n\nPlease choose a different project name.')
    );
    process.exit(1);
  }
}

这个函数用了一个外部依赖来校验文件名是否符合npm包文件名的规范，而后定义了三个不能取得名字react、react-dom、react-scripts，红色框出来的，以前引用的是一个函数依赖printValidationResults(),最新的代码里面换成了ES6属性spread,不过这个属性在ES9里也有新的用法

printValidationResults()：函数引用，这个函数就是我说的特别简单的类型，里面就是把接收到的错误信息循环打印出来

isSafeToCreateProjectIn

function isSafeToCreateProjectIn(root, name) {
  const validFiles = [
    '.DS_Store',
    '.git',
    '.gitattributes',
    '.gitignore',
    '.gitlab-ci.yml',
    '.hg',
    '.hgcheck',
    '.hgignore',
    '.idea',
    '.npmignore',
    '.travis.yml',
    'docs',
    'LICENSE',
    'README.md',
    'mkdocs.yml',
    'Thumbs.db',
  ];
  // These files should be allowed to remain on a failed install, but then
  // silently removed during the next create.
  const errorLogFilePatterns = [
    'npm-debug.log',
    'yarn-error.log',
    'yarn-debug.log',
  ];
  const isErrorLog = file => {
    return errorLogFilePatterns.some(pattern => file.startsWith(pattern));
  };

  const conflicts = fs
    .readdirSync(root)
    .filter(file => !validFiles.includes(file))
    // IntelliJ IDEA creates module files before CRA is launched
    .filter(file => !/\.iml$/.test(file))
    // Don't treat log files from previous installation as conflicts
    .filter(file => !isErrorLog(file));

  if (conflicts.length > 0) {
    console.log(
      `The directory ${chalk.green(name)} contains files that could conflict:`
    );
    console.log();
    for (const file of conflicts) {
      try {
        const stats = fs.lstatSync(path.join(root, file));
        if (stats.isDirectory()) {
          console.log(`  ${chalk.blue(`${file}/`)}`);
        } else {
          console.log(`  ${file}`);
        }
      } catch (e) {
        console.log(`  ${file}`);
      }
    }
    console.log();
    console.log(
      'Either try using a new directory name, or remove the files listed above.'
    );

    return false;
  }

  // Remove any log files from a previous installation.
  fs.readdirSync(root).forEach(file => {
    if (isErrorLog(file)) {
      fs.removeSync(path.join(root, file));
    }
  });
  return true;
}

安全性校验，检查当前目录下是否存在已有文件,判断建立的这个目录是否包含除了上述validFiles里面的文件

shouldUseYarn

function shouldUseYarn() {
  try {
    execSync('yarnpkg --version', { stdio: 'ignore' });
    return true;
  } catch (e) {
    return false;
  }
}

execSync是由node自身模块child_process引用而来，用来执行命令的，这个函数执行yarnpkg --version来判断咱们是否正确安装了yarn，若是没有正确安装yarn的话，useYarn依然为false，无论指没有指定--use-npm。

• execSync：引用自child_process.execSync，用于执行须要执行的子进程

checkThatNpmCanReadCwd

// See https://github.com/facebook/create-react-app/pull/3355
function checkThatNpmCanReadCwd() {
  const cwd = process.cwd();// 当前的进程目录
  let childOutput = null; // 保存npm信息
  try {
    // Note: intentionally using spawn over exec since
    // the problem doesn't reproduce otherwise.
    // `npm config list` is the only reliable way I could find
    // to reproduce the wrong path. Just printing process.cwd()
    // in a Node process was not enough.
    childOutput = spawn.sync('npm', ['config', 'list']).output.join('');
    // 至关于执行`npm config list`并将其输出的信息组合成为一个字符串
  } catch (err) {
    // Something went wrong spawning node.
    // Not great, but it means we can't do this check.
    // We might fail later on, but let's continue.
    return true;
  }
  if (typeof childOutput !== 'string') {
    return true;
  }
  //字符串换行分割
  const lines = childOutput.split('\n');
  // `npm config list` output includes the following line:
  // "; cwd = C:\path\to\current\dir" (unquoted)
  // I couldn't find an easier way to get it.
  const prefix = '; cwd = ';// 定义须要的信息前缀
  const line = lines.find(line => line.startsWith(prefix));// 取整个lines里面的每一个line查找有没有这个前缀的一行
  if (typeof line !== 'string') {
    // Fail gracefully. They could remove it.
    return true;
  }
  const npmCWD = line.substring(prefix.length);
  if (npmCWD === cwd) {// 判断当前目录和执行目录是否一致
    return true;
  }
  console.error(
    chalk.red( // 不一致就打印如下信息，大概意思就是`npm`进程没有在正确的目录下执行
      `Could not start an npm process in the right directory.\n\n` +
        `The current directory is: ${chalk.bold(cwd)}\n` +
        `However, a newly started npm process runs in: ${chalk.bold(
          npmCWD
        )}\n\n` +
        `This is probably caused by a misconfigured system terminal shell.`
    )
  );
  if (process.platform === 'win32') {// 对window的状况做了单独判断
    console.error(
      chalk.red(`On Windows, this can usually be fixed by running:\n\n`) +
        `  ${chalk.cyan(
          'reg'
        )} delete "HKCU\\Software\\Microsoft\\Command Processor" /v AutoRun /f\n` +
        `  ${chalk.cyan(
          'reg'
        )} delete "HKLM\\Software\\Microsoft\\Command Processor" /v AutoRun /f\n\n` +
        chalk.red(`Try to run the above two lines in the terminal.\n`) +
        chalk.red(
          `To learn more about this problem, read: https://blogs.msdn.microsoft.com/oldnewthing/20071121-00/?p=24433/`
        )
    );
  }
  return false;
}

上述代码表示已经解析了，其中用到了一个外部依赖：

cross-spawn：用来执行node进程，Node跨平台解决方案，解决在windows下各类问题npm地址

checkNpmVersion

function checkNpmVersion() {
  let hasMinNpm = false;
  let npmVersion = null;
  try {
    npmVersion = execSync('npm --version')
      .toString()
      .trim();
    hasMinNpm = semver.gte(npmVersion, '5.0.0');
  } catch (err) {
    // ignore
  }
  return {
    hasMinNpm: hasMinNpm,
    npmVersion: npmVersion,
  };
}

检测node版本，react-scrpts是须要依赖Node版本的，低版本的Node不支持，版本比较使用的是一个semver package.

run

run 主要作的事情就是安装依赖、拷贝模板。
run()函数在createApp()函数的全部内容执行完毕后执行，它接收7个参数。

• root：咱们建立的目录的绝对路径
• appName：咱们建立的目录名称
• version；react-scripts的版本
• verbose：继续传入verbose，在createApp中没有使用到
• originalDirectory：原始目录，这个以前说到了，到run函数中就有用了
• tempalte：模板，这个参数以前也说过了，不对外使用
• useYarn：是否使用yarn
• usePnp: 是否使用pnp

function run(
  root,
  appName,
  version,
  verbose,
  originalDirectory,
  template,
  useYarn,
  usePnp
) {
  Promise.all([
    getInstallPackage(version, originalDirectory), //获取依赖安装包信息
    getTemplateInstallPackage(template, originalDirectory),// 获取模板安装包信息
  ]).then(([packageToInstall, templateToInstall]) => {
    const allDependencies = ['react', 'react-dom', packageToInstall];

    console.log('Installing packages. This might take a couple of minutes.');

    Promise.all([
      // 从网址或路径中提取软件包名称，也就是获取安装包名称这里以前用的getPackageName()
      getPackageInfo(packageToInstall),
      getPackageInfo(templateToInstall),
    ])
      .then(([packageInfo, templateInfo]) =>
        checkIfOnline(useYarn).then(isOnline => ({
          isOnline,
          packageInfo,
          templateInfo,
        }))
      )
      .then(({ isOnline, packageInfo, templateInfo }) => {
        let packageVersion = semver.coerce(packageInfo.version);

        const templatesVersionMinimum = '3.3.0';

        // Assume compatibility if we can't test the version.
        if (!semver.valid(packageVersion)) {
          packageVersion = templatesVersionMinimum;
        }

        // Only support templates when used alongside new react-scripts versions.
        const supportsTemplates = semver.gte(
          packageVersion,
          templatesVersionMinimum
        );
        if (supportsTemplates) {
          allDependencies.push(templateToInstall);
        } else if (template) {
          console.log('');
          console.log(
            `The ${chalk.cyan(packageInfo.name)} version you're using ${
              packageInfo.name === 'react-scripts' ? 'is not' : 'may not be'
            } compatible with the ${chalk.cyan('--template')} option.`
          );
          console.log('');
        }

        // TODO: Remove with next major release.
        if (!supportsTemplates && (template || '').includes('typescript')) {
          allDependencies.push(
            '@types/node',
            '@types/react',
            '@types/react-dom',
            '@types/jest',
            'typescript'
          );
        }

        console.log(
          `Installing ${chalk.cyan('react')}, ${chalk.cyan(
            'react-dom'
          )}, and ${chalk.cyan(packageInfo.name)}${
            supportsTemplates ? ` with ${chalk.cyan(templateInfo.name)}` : ''
          }...`
        );
        console.log();
        // 安装依赖
        return install(
          root,
          useYarn,
          usePnp,
          allDependencies,
          verbose,
          isOnline
        ).then(() => ({
          packageInfo,
          supportsTemplates,
          templateInfo,
        }));
      })
      .then(async ({ packageInfo, supportsTemplates, templateInfo }) => {
        const packageName = packageInfo.name;
        const templateName = supportsTemplates ? templateInfo.name : undefined;
        checkNodeVersion(packageName);// 判断node_modules下面全部包中对于node版本的最低要求
        setCaretRangeForRuntimeDeps(packageName);// 给package.json中的依赖添加^

        const pnpPath = path.resolve(process.cwd(), '.pnp.js');

        const nodeArgs = fs.existsSync(pnpPath) ? ['--require', pnpPath] : [];
         // 安装依赖同时copy react-scripts下面的template到当前目录
        await executeNodeScript(
          {
            cwd: process.cwd(),
            args: nodeArgs,
          },
          [root, appName, verbose, originalDirectory, templateName],
          `
        var init = require('${packageName}/scripts/init.js');
        init.apply(null, JSON.parse(process.argv[1]));
      `
        );

        if (version === 'react-scripts@0.9.x') {
          console.log(
            chalk.yellow(
              `\nNote: the project was bootstrapped with an old unsupported version of tools.\n` +
                `Please update to Node >=8.10 and npm >=5 to get supported tools in new projects.\n`
            )
          );
        }
      })
      .catch(reason => {
        console.log();
        console.log('Aborting installation.');
        if (reason.command) {
          console.log(`  ${chalk.cyan(reason.command)} has failed.`);
        } else {
          console.log(
            chalk.red('Unexpected error. Please report it as a bug:')
          );
          console.log(reason);
        }
        console.log();

        // On 'exit' we will delete these files from target directory.
        // 在“退出”时，咱们将从目标目录中删除这些文件
        const knownGeneratedFiles = [
          'package.json',
          'yarn.lock',
          'node_modules',
        ];
        const currentFiles = fs.readdirSync(path.join(root));
        currentFiles.forEach(file => {
          knownGeneratedFiles.forEach(fileToMatch => {
            // This removes all knownGeneratedFiles.
            if (file === fileToMatch) {
              console.log(`Deleting generated file... ${chalk.cyan(file)}`);
              fs.removeSync(path.join(root, file));
            }
          });
        });
        const remainingFiles = fs.readdirSync(path.join(root));
        if (!remainingFiles.length) {//判断当前目录下是否还存在文件
          // Delete target folder if empty
          console.log(
            `Deleting ${chalk.cyan(`${appName}/`)} from ${chalk.cyan(
              path.resolve(root, '..')
            )}`
          );
          process.chdir(path.resolve(root, '..'));
          fs.removeSync(path.join(root));
        }
        console.log('Done.');
        process.exit(1);
      });
  });
}

run在这里对react-script作了不少处理，大概是因为react-script自己是有node版本的依赖的，并且在用create-react-app init <project>初始化一个项目的时候，是能够指定react-script的版本;简单来讲run 主要作的事情就是安装依赖、拷贝模板。

其中函数列表：

• getInstallPackage()：获取要安装的react-scripts版本或者开发者本身定义的react-scripts。
  
• getTemplateInstallPackage: 获取模板安装包信息，根据选择的模板建立模板安装包名
  
  
• getPackageInfo()： 从网址或路径中提取软件包名称，也就是获取安装包名称这里以前用的getPackageName()

• checkIfOnline()：检查网络链接是否正常
• install()：安装开发依赖包，
• checkNodeVersion()：检查Node版本信息，判断node_modules下面全部包中对于node版本的最低要求
• setCaretRangeForRuntimeDeps()：检查发开依赖是否正确安装，版本是否正确
• executeNodeScript()： 安装依赖同时copy react-scripts下面的template到当前目录，在create-react-app以前的版本中，这里是经过调用react-script下的init方法来执行后续动做的。这里经过调用executeNodeScript方法

getInstallPackage

function getInstallPackage(version, originalDirectory) {
  let packageToInstall = 'react-scripts';
  const validSemver = semver.valid(version);
  if (validSemver) {
    packageToInstall += `@${validSemver}`;
  } else if (version) {
    if (version[0] === '@' && !version.includes('/')) {
      packageToInstall += version;
    } else if (version.match(/^file:/)) {
      packageToInstall = `file:${path.resolve(
        originalDirectory,
        version.match(/^file:(.*)?$/)[1]
      )}`;
    } else {
      // for tar.gz or alternative paths
      packageToInstall = version;
    }
  }

  const scriptsToWarn = [
    {
      name: 'react-scripts-ts',
      message: chalk.yellow(
        `The react-scripts-ts package is deprecated. TypeScript is now supported natively in Create React App. You can use the ${chalk.green(
          '--template typescript'
        )} option instead when generating your app to include TypeScript support. Would you like to continue using react-scripts-ts?`
      ),
    },
  ];

  for (const script of scriptsToWarn) {
    if (packageToInstall.startsWith(script.name)) {
      return inquirer
        .prompt({
          type: 'confirm',
          name: 'useScript',
          message: script.message,
          default: false,
        })
        .then(answer => {
          if (!answer.useScript) {
            process.exit(0);
          }

          return packageToInstall;
        });
    }
  }

  return Promise.resolve(packageToInstall);
}

getInstallPackage根据传入的 version 和原始路径 originalDirectory 去获取要安装的 package 列表，默认状况下version 为 undefined，获取到的 packageToInstall 为react-scripts,也就是咱们如上图的 resolve 回调

getTemplateInstallPackage

function getTemplateInstallPackage(template, originalDirectory) {
  let templateToInstall = 'cra-template';
  if (template) {
    if (template.match(/^file:/)) {
      templateToInstall = `file:${path.resolve(
        originalDirectory,
        template.match(/^file:(.*)?$/)[1]
      )}`;
    } else if (
      template.includes('://') ||
      template.match(/^.+\.(tgz|tar\.gz)$/)
    ) {
      // for tar.gz or alternative paths
      templateToInstall = template;
    } else {
      // Add prefix 'cra-template-' to non-prefixed templates, leaving any
      // @scope/ intact.
      const packageMatch = template.match(/^(@[^/]+\/)?(.+)$/);
      const scope = packageMatch[1] || '';
      const templateName = packageMatch[2];

      const name = templateName.startsWith(templateToInstall)
        ? templateName
        : `${templateToInstall}-${templateName}`;
      templateToInstall = `${scope}${name}`;
    }
  }

  return Promise.resolve(templateToInstall);
}

getTemplateInstallPackage建立一个cra-template模板前缀，把传入的模板名称合并返回一个新的模板名称，

getPackageInfo

// Extract package name from tarball url or path.
// 从网址或路径中提取软件包名称
function getPackageInfo(installPackage) {
  if (installPackage.match(/^.+\.(tgz|tar\.gz)$/)) {// 判断`react-scripts`的信息来安装这个包，用于返回正规的包名
    return getTemporaryDirectory() //建立一个临时目录
      .then(obj => {
        let stream;
        if (/^http/.test(installPackage)) {
          stream = hyperquest(installPackage);
        } else {
          stream = fs.createReadStream(installPackage);
        }
        return extractStream(stream, obj.tmpdir).then(() => obj);
      })
      .then(obj => {
        const { name, version } = require(path.join(
          obj.tmpdir,
          'package.json'
        ));
        obj.cleanup();
        return { name, version };
      })
      .catch(err => {
        // The package name could be with or without semver version, e.g. react-scripts-0.2.0-alpha.1.tgz
        // However, this function returns package name only without semver version.
        console.log(
          `Could not extract the package name from the archive: ${err.message}`
        );
        const assumedProjectName = installPackage.match(
          /^.+\/(.+?)(?:-\d+.+)?\.(tgz|tar\.gz)$/
        )[1];
        console.log(
          `Based on the filename, assuming it is "${chalk.cyan(
            assumedProjectName
          )}"`
        );
        return Promise.resolve({ name: assumedProjectName });
      });
  } else if (installPackage.startsWith('git+')) { // 此处为信息中包含`git+`信息的状况
    // Pull package name out of git urls e.g:
    // git+https://github.com/mycompany/react-scripts.git
    // git+ssh://github.com/mycompany/react-scripts.git#v1.2.3
    return Promise.resolve({
      name: installPackage.match(/([^/]+)\.git(#.*)?$/)[1],
    });
  } else if (installPackage.match(/.+@/)) { // 此处为只有版本信息的时候的状况
    // Do not match @scope/ when stripping off @version or @tag
    return Promise.resolve({
      name: installPackage.charAt(0) + installPackage.substr(1).split('@')[0],
      version: installPackage.split('@')[1],
    });
  } else if (installPackage.match(/^file:/)) {  // 此处为信息中包含`file:`开头的状况
    const installPackagePath = installPackage.match(/^file:(.*)?$/)[1];
    const { name, version } = require(path.join(
      installPackagePath,
      'package.json'
    ));
    return Promise.resolve({ name, version });
  }
  return Promise.resolve({ name: installPackage });
}

这个函数的做用就是返回正常的包名，不带任何符号的，这里使用了一个外部依赖hyperquest，看了下之前版本的源码，这个函数以前是
getPackageName()同一个方法

install

function install(root, useYarn, usePnp, dependencies, verbose, isOnline) {
  return new Promise((resolve, reject) => {  // 封装在一个回调函数中
    let command;// 定义一个命令
    let args;// 定义一个命令的参数
    if (useYarn) { // 若是使用yarn
      command = 'yarnpkg';
      args = ['add', '--exact'];
      if (!isOnline) {
        args.push('--offline'); // 是否离线模式
      }
      if (usePnp) {
        args.push('--enable-pnp');
      }
      [].push.apply(args, dependencies); // 组合参数和开发依赖 `react` `react-dom` `react-scripts`

      // Explicitly set cwd() to work around issues like
      // https://github.com/facebook/create-react-app/issues/3326.
      // Unfortunately we can only do this for Yarn because npm support for
      // equivalent --prefix flag doesn't help with this issue.
      // This is why for npm, we run checkThatNpmCanReadCwd() early instead.
      args.push('--cwd');// 指定命令执行目录的地址
      args.push(root);// 地址的绝对路径

      if (!isOnline) { // 离线模式时候会发出警告
        console.log(chalk.yellow('You appear to be offline.'));
        console.log(chalk.yellow('Falling back to the local Yarn cache.'));
        console.log();
      }
    } else { //使用npm 的状况
      command = 'npm';
      args = [
        'install',
        '--save',
        '--save-exact',
        '--loglevel',
        'error',
      ].concat(dependencies);

      if (usePnp) { // 若是是pnp发出警告npm 不支持pnp
        console.log(chalk.yellow("NPM doesn't support PnP."));
        console.log(chalk.yellow('Falling back to the regular installs.'));
        console.log();
      }
    }

    if (verbose) {
      args.push('--verbose');
    }
    // 在spawn执行完命令后会有一个回调，判断code是否为 0，而后 resolve Promise，
    const child = spawn(command, args, { stdio: 'inherit' });
    child.on('close', code => {
      if (code !== 0) {
        reject({
          command: `${command} ${args.join(' ')}`,
        });
        return;
      }
      resolve();
    });
  });
}

install就是把梳理好的package交给npm或者yarn安装依赖

executeNodeScript

function executeNodeScript({ cwd, args }, data, source) {
  return new Promise((resolve, reject) => {
    const child = spawn(
      process.execPath,
      [...args, '-e', source, '--', JSON.stringify(data)],
      { cwd, stdio: 'inherit' }
    );

    child.on('close', code => {
      if (code !== 0) {
        reject({
          command: `node ${args.join(' ')}`,
        });
        return;
      }
      resolve();
    });
  });
}

executeNodeScript方法主要是经过 spawn 来经过 node命令执行react-script下的 init 方法

react-script/init.js

module.exports = function(
  appPath,
  appName,
  verbose,
  originalDirectory,
  templateName
) {
  const appPackage = require(path.join(appPath, 'package.json')); //项目目录下的 package.json
  const useYarn = fs.existsSync(path.join(appPath, 'yarn.lock')); //经过判断目录下是否有 yarn.lock 来判断是否使用 yarn

  if (!templateName) { // 判断是否有模板名称
    console.log('');
    console.error(
      `A template was not provided. This is likely because you're using an outdated version of ${chalk.cyan(
        'create-react-app'
      )}.`
    );
    console.error(
      `Please note that global installs of ${chalk.cyan(
        'create-react-app'
      )} are no longer supported.`
    );
    return;
  }

  const templatePath = path.join( //获取模板的路径
    require.resolve(templateName, { paths: [appPath] }),
    '..'
  );

  let templateJsonPath;
  if (templateName) {  //
    templateJsonPath = path.join(templatePath, 'template.json');
  } else {
    // TODO: Remove support for this in v4.
    templateJsonPath = path.join(appPath, '.template.dependencies.json');
  }

  let templateJson = {};
  if (fs.existsSync(templateJsonPath)) { //判断路径是否正确
    templateJson = require(templateJsonPath);
  }

  // Copy over some of the devDependencies
  appPackage.dependencies = appPackage.dependencies || {};

  // Setup the script rules 定义scripts
  const templateScripts = templateJson.scripts || {};
  appPackage.scripts = Object.assign(
    {
      start: 'react-scripts start',
      build: 'react-scripts build',
      test: 'react-scripts test',
      eject: 'react-scripts eject',
    },
    templateScripts
  );

  // Update scripts for Yarn users
  if (useYarn) {// 判断是否使用yarn，若是是替换成你怕吗 npm 
    appPackage.scripts = Object.entries(appPackage.scripts).reduce(
      (acc, [key, value]) => ({
        ...acc,
        [key]: value.replace(/(npm run |npm )/, 'yarn '),
      }),
      {}
    );
  }

  // Setup the eslint config 设置eslint配置
  appPackage.eslintConfig = {
    extends: 'react-app',
  };

  // Setup the browsers list  这是浏览器 openBrowser
  appPackage.browserslist = defaultBrowsers;

  fs.writeFileSync( //写入咱们须要建立的目录下的 package.json 中
    path.join(appPath, 'package.json'),
    JSON.stringify(appPackage, null, 2) + os.EOL
  );

  // 判断项目目录是否有`README.md`，模板目录中已经定义了`README.md`防止冲突
  const readmeExists = fs.existsSync(path.join(appPath, 'README.md'));
  if (readmeExists) {
    fs.renameSync(
      path.join(appPath, 'README.md'),
      path.join(appPath, 'README.old.md')
    );
  }

  // Copy the files for the user
  const templateDir = path.join(templatePath, 'template');
  if (fs.existsSync(templateDir)) {
    fs.copySync(templateDir, appPath);
  } else {
    console.error(
      `Could not locate supplied template: ${chalk.green(templateDir)}`
    );
    return;
  }

  // modifies README.md commands based on user used package manager.
  if (useYarn) {// 判断是否使用yarn，若是是替换成你怕吗 npm 默认使用npm
    try {
      const readme = fs.readFileSync(path.join(appPath, 'README.md'), 'utf8');
      fs.writeFileSync(
        path.join(appPath, 'README.md'),
        readme.replace(/(npm run |npm )/g, 'yarn '),
        'utf8'
      );
    } catch (err) {
      // Silencing the error. As it fall backs to using default npm commands.
    }
  }

  const gitignoreExists = fs.existsSync(path.join(appPath, '.gitignore'));
  if (gitignoreExists) {
    // Append if there's already a `.gitignore` file there
    const data = fs.readFileSync(path.join(appPath, 'gitignore'));
    fs.appendFileSync(path.join(appPath, '.gitignore'), data);
    fs.unlinkSync(path.join(appPath, 'gitignore'));
  } else {
    // Rename gitignore after the fact to prevent npm from renaming it to .npmignore
    // See: https://github.com/npm/npm/issues/1862
    fs.moveSync(
      path.join(appPath, 'gitignore'),
      path.join(appPath, '.gitignore'),
      []
    );
  }

  let command;
  let remove;
  let args;

  if (useYarn) {
    command = 'yarnpkg';
    remove = 'remove';
    args = ['add'];
  } else {
    command = 'npm';
    remove = 'uninstall';
    args = ['install', '--save', verbose && '--verbose'].filter(e => e);
  }

  // Install additional template dependencies, if present 安装其余模板依赖项若是有
  const templateDependencies = templateJson.dependencies;
  if (templateDependencies) {
    args = args.concat(
      Object.keys(templateDependencies).map(key => {
        return `${key}@${templateDependencies[key]}`;
      })
    );
  }

  // Install react and react-dom for backward compatibility with old CRA cli
  // which doesn't install react and react-dom along with react-scripts
  if (!isReactInstalled(appPackage)) {
    args = args.concat(['react', 'react-dom']);
  }
  // 安装react和react-dom以便与旧CRA cli向后兼容
  // 没有安装react和react-dom以及react-scripts
  // 或模板是presetend（经过--internal-testing-template）

  // Install template dependencies, and react and react-dom if missing.
  if ((!isReactInstalled(appPackage) || templateName) && args.length > 1) {
    console.log();
    console.log(`Installing template dependencies using ${command}...`);

    const proc = spawn.sync(command, args, { stdio: 'inherit' });
    if (proc.status !== 0) {
      console.error(`\`${command} ${args.join(' ')}\` failed`);
      return;
    }
  }

  if (args.find(arg => arg.includes('typescript'))) {
    console.log();
    verifyTypeScriptSetup();
  }

  // Remove template
  console.log(`Removing template package using ${command}...`);
  console.log();

  const proc = spawn.sync(command, [remove, templateName], {
    stdio: 'inherit',
  });
  if (proc.status !== 0) {
    console.error(`\`${command} ${args.join(' ')}\` failed`);
    return;
  }

  if (tryGitInit(appPath)) {
    console.log();
    console.log('Initialized a git repository.');
  }

  // Display the most elegant way to cd.
  // This needs to handle an undefined originalDirectory for
  // backward compatibility with old global-cli's.
  // 显示最优雅的CD方式。
  // 这须要处理一个未定义的originalDirectory
  // 与旧的global-cli的向后兼容性。
  let cdpath;
  if (originalDirectory && path.join(originalDirectory, appName) === appPath) {
    cdpath = appName;
  } else {
    cdpath = appPath;
  }

  // Change displayed command to yarn instead of yarnpkg
  // 将显示的命令更改成yarn而不是yarnpkg
  const displayedCommand = useYarn ? 'yarn' : 'npm';

  console.log();
  console.log(`Success! Created ${appName} at ${appPath}`);
  console.log('Inside that directory, you can run several commands:');
  console.log();
  console.log(chalk.cyan(`  ${displayedCommand} start`));
  console.log('    Starts the development server.');
  console.log();
  console.log(
    chalk.cyan(`  ${displayedCommand} ${useYarn ? '' : 'run '}build`)
  );
  console.log('    Bundles the app into static files for production.');
  console.log();
  console.log(chalk.cyan(`  ${displayedCommand} test`));
  console.log('    Starts the test runner.');
  console.log();
  console.log(
    chalk.cyan(`  ${displayedCommand} ${useYarn ? '' : 'run '}eject`)
  );
  console.log(
    '    Removes this tool and copies build dependencies, configuration files'
  );
  console.log(
    '    and scripts into the app directory. If you do this, you can’t go back!'
  );
  console.log();
  console.log('We suggest that you begin by typing:');
  console.log();
  console.log(chalk.cyan('  cd'), cdpath);
  console.log(`  ${chalk.cyan(`${displayedCommand} start`)}`);
  if (readmeExists) {
    console.log();
    console.log(
      chalk.yellow(
        'You had a `README.md` file, we renamed it to `README.old.md`'
      )
    );
  }
  console.log();
  console.log('Happy hacking!');
}

初始化方法主要作的事情就是修改目标路径下的 package.json，添加一些配置命令，而后 copy！react-script 下的模板到目标路径下

项目初始化完成

简单总结下

• 判断 node 版本，若是大版本小于 8 ，则直接退出（截止目前是 8）
• createReactApp.js 初始化一些命令参数，而后再去判断是否传入了 packageName，不然直接退出
• 各类版本的判断，而后经过cross-spawn来用命令行执行全部的安装
• 当全部的依赖安装完后，依旧经过命令行，初始化 node 环境，来执行 react-script 下的初始化方法：修改 package.json 中的一些配置、以及 copy 模板文件
• 处理完成，给出用户友好提示

看完大佬的分享，在本身跑一遍果真理顺不少，感谢大佬的分享，写出来也是记录自我一个学习的过程，方便后期查看