Interpretation of /packages/react-scripts of the core source code of create-react-app scaffolding

React Official Scaffolding

• Take version 5.0.1 as an example
• Create a project execution process

Source code interpretation debug

Create a project create-react-app my-app, interpret the previous /packages/create-react-appsource code, you can interpret it from the pacakage/create-react-app core source code of create-react-app in detail (1)

Equivalent to packages/react-scriptsrunning the command:

yarn init

Below scripts/init.js, the code executes parsing on demand from top to bottom

1. Enter the function

 const appPackage = require(path.join(appPath, 'package.json'));

• debugcode show as below:

• Then execute and useyarnreturn , because the dependencies of the installation falseused earliernpm
• templateNameThe value is cra-template;
• templatePathThe running value is 'my-app/node_modules/cra-template';
• templateJsonPathoperating value'my-app/node_modules/cra-template/template.json'
• Get templateJsonthe read value as:

2. templatePackageToReplace

execute returnfalse

3. Add in the new my-appproject , the specific source code is as follows:package.jsonscripts

appPackage.scripts = Object.assign(
    {
    
    
      start: 'react-scripts start',
      build: 'react-scripts build',
      test: 'react-scripts test',
      eject: 'react-scripts eject',
    },
    templateScripts
  );

Is it familiar here? create-react-appThe project initialized by scaffolding package.jsonis like this

4. Set eslint config

 appPackage.eslintConfig = {
    
    
   extends: 'react-app',
 };

5. Set the browsers list

6. Asynchronous writepackage.json

fs.writeFileSync(
    path.join(appPath, 'package.json'),
    JSON.stringify(appPackage, null, 2) + os.EOL
  );

After the execution is complete, go to the newly created project my-appto view the following:

• Determine whether it exists README.md, returnfalse

8. Copy the template project to the new project directory

In create-react-app/packagesthe directory, you can see the project template cra-templatefor initialization

• templateDirThe operating value is'my-app/node_modules/cra-template/template'
• appPathThe operating value is'/Users/coco/project/shiqiang/create-react-app/packages/my-app'
• Source Code Execution Copy

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;
  }

After running, go my-appto view, the directory at this time is as follows:

.gitignorefile does not exist

9. Determine whether it exists.gitignore

The source code is as follows:

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'),
      []
    );
  }

Return false, then enter else, the operation is completed, and the new project gitignoreis replaced with.gitignore

10. Initializationgit repo

The source code is as follows:

function tryGitInit() {
    
    
  try {
    
    
    execSync('git --version', {
    
     stdio: 'ignore' });
    if (isInGitRepository() || isInMercurialRepository()) {
    
    
      return false;
    }

    execSync('git init', {
    
     stdio: 'ignore' });
    return true;
  } catch (e) {
    
    
    console.warn('Git repo not initialized', e);
    return false;
  }
}

• yarn ornpm

  if (useYarn) {
    
    
    command = 'yarnpkg';
    remove = 'remove';
    args = ['add'];
  } else {
    
    
    command = 'npm';
    remove = 'uninstall';
    args = [
      'install',
      '--no-audit', // https://github.com/facebook/create-react-app/issues/11174
      '--save',
      verbose && '--verbose',
    ].filter(e => e);
  }

• Install additional template dependencies (if present)

const dependenciesToInstall = Object.entries({
    
    
    ...templatePackage.dependencies,
    ...templatePackage.devDependencies,
  });
  if (dependenciesToInstall.length) {
    
    
    args = args.concat(
      dependenciesToInstall.map(([dependency, version]) => {
    
    
        return `${
      
      dependency}@${
      
      version}`;
      })
    );
  }

debugdata:

argsOperating data:

11. Determine whether to install react

• The source code is as follows:

 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;
    }
  }

• functionisReactInstalled

function isReactInstalled(appPackage) {
    
    
  const dependencies = appPackage.dependencies || {
    
    };

  return (
    typeof dependencies.react !== 'undefined' &&
    typeof dependencies['react-dom'] !== 'undefined'
  );
}

• Key print information:
  

12. The child process executes the installation command

• The source code is as follows:

 const proc = spawn.sync(command, args, {
    
     stdio: 'inherit' });

• The console operation information is as follows:

13. Execute delete, delete node_modulesthe directorycra-template

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14. Show the most elegant way to cd

• The source code is as follows:

 let cdpath;
  if (originalDirectory && path.join(originalDirectory, appName) === appPath) {
    
    
    cdpath = appName;
  } else {
    
    
    cdpath = appPath;
  }

After running cdpaththe value ismy-app

15. Success message prompt printing

• The source code is as follows:

 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!');

• The console print information is as follows:

At this point, react-scriptsthe completion of the new project