function check (src, operation) {
  const match = operation.match(/^(!?)([a-z]*)([<>=]*)(\d*)$/)

  if (match) {
    const isNotSubstr = match[1]
    const mainSubstr = match[2]
    const compareSubstr = match[3]
    const numberSubstr = match[4]

    let result
    if (mainSubstr === 'empty') {
      result = src === ''
    } else if (mainSubstr === 'length' && compareSubstr && numberSubstr) {
      const number = Number(numberSubstr)
      if (compareSubstr === '<=') {
        result = src.length <= number
      } else {
        return false
      }
    } else {
      return false
    }

    if (isNotSubstr) {
      result = !result
    }

    return result
  }
}

console.log(check('aaa', '!length<=10'))