transform-business-hours.js

const days = [
  'mon', 'tue', 'wed', 'thu', 'fri', 'sat', 'sun'
]
const data = {
  'mon': [
    {
      start: '11:00',
      end: '22:00'
    }
  ],
  'wed': [
    {
      start: '11:00',
      end: '22:00'
    }
  ],
  tue: [
    {
      start: '11:00',
      end: '22:00'
    }
  ],
  'thu': [
    {
      start: '11:00',
      end: '22:00'
    }
  ],
  'fri': [],
  'sat': [],
  'sun': []
}

let result = []
let lastIndex = 0

days
  .forEach((day, index) => {
    const currentBusinessHours = data[day]

    // push first item into array
    if (index === 0) {
      return result.push({
        businessHours: currentBusinessHours,
        days: [ day ]
      })
    }

    const previousDay = days[index - 1]
    const previousBusinessHours = data[previousDay]

    if (JSON.stringify(previousBusinessHours) === JSON.stringify(currentBusinessHours)) {
      return result[lastIndex].days.push(day)
    }

    lastIndex += 1

    return result.push({
      businessHours: currentBusinessHours == null
        ? []
        : currentBusinessHours,
      days: [ day ]
    })
  })

console.log(JSON.stringify(result))
// result will be:
// [
//   {
//     "businessHours": [
//       {
//         "start": "11:00",
//         "end": "22:00"
//       }
//     ],
//     "days": [
//       "mon",
//       "tue",
//       "wed",
//       "thu"
//     ]
//   },
//   {
//     "businessHours": [],
//     "days": [
//       "fri",
//       "sat",
//       "sun"
//     ]
//   }
// ]