在其他块中，这些额外的花括号的用途是什么？

Question

我正在查看一些类型代码，我看到在一个其他块中使用了额外的花括号。这些额外的支架有什么用处吗？还是简单地将额外的分组添加到两个几乎相同的代码片段中？鉴于这是一个非常流行的微软回购，它怀疑它的意外。

  if (playwrightTestPackagePath) {
    require(playwrightTestPackagePath).addTestCommand(program);
    require(playwrightTestPackagePath).addShowReportCommand(program);
    require(playwrightTestPackagePath).addListFilesCommand(program);
  } else {
    {
      const command = program.command('test').allowUnknownOption(true);
      command.description('Run tests with Playwright Test. Available in @playwright/test package.');
      command.action(async () => {
        console.error('Please install @playwright/test package to use Playwright Test.');
        console.error('  npm install -D @playwright/test');
        process.exit(1);
      });
    }

    {
      const command = program.command('show-report').allowUnknownOption(true);
      command.description('Show Playwright Test HTML report. Available in @playwright/test package.');
      command.action(async () => {
        console.error('Please install @playwright/test package to use Playwright Test.');
        console.error('  npm install -D @playwright/test');
        process.exit(1);
      });
    }
  }
}

来源

Answer 1

它只是为变量创建新范围的块。您可以看到const command = ... --这不可能在一个范围内，否则会引发错误：SyntaxError: redeclaration of const command。

// no errors
{
  const x = 1;
  console.log(x) // 1
}
{
  const x = 2;
  console.log(x) // 2
}
{
  const x = 3;
  console.log(x) // 3
}

// error
const x = 1
const x = 2 // Uncaught SyntaxError: redeclaration of const x
const x = 3

我认为这只是为了避免命名像command2, command3等。