regex-parse-filenames-and-extensions.js

function testFilename(filename) {
  const match = filename.match(/^(?:(\d+)[.-])?([^.]+)(?:\.([^.]+))?(?:\.([^.]+))?$/)
  
  if (match) {
    const order = match[1]
    const base = match[2] ?? filename
    const modifier = match[4] ? match[3] : undefined
    const extension = match[4] ?? match[3]
    
    console.log({
      filename,
      order,
      base,
      modifier,
      extension
    })
  }
}

// Examples with parsed values:
testFilename('01-hello.md')        // {order: '01', base: 'hello', modifier: undefined, extension: 'md'}
testFilename('hello.md')
testFilename('hello.test.js')      // {order: undefined, base: 'hello', modifier: 'test', extension: 'js'}
testFilename('01.page.test.jsx')
testFilename('hello')
testFilename('wow/hello.md')