domain.js

input = [
      ['google.com', '20'],
      ['mail.google.com', '10'],
      ['zhenghao.mail.google.com', '10'],
]

output = { 'google.com': 40, 
  'mail.google.com': 20, 
  'zhenghao.mail.google.com': 10 } 
  
function fn(array) {
    return array.reduce((result, [url, count]) => {
      const urlArr = url.split('.')
      for (let i = urlArr.length - 2; i >= 0; i--) {
        const domain = urlArr.slice(i).join('.')
        result[domain] = (result[domain] || 0) + Number(count)
      }
      return result
    }, {})
  }