const result = {}

​

const dateArr = ['2021-08-06', '2021-11-06', '2021-08-06', '2021-13-06']

​

// Loop through each item in the dateArr array

for (let i = 0; i < dateArr.length; i++) {

  // Get the value for the current iteration of the loop

  const date = dateArr[i]

  // If the results array hasn't seen this value before then define it.

  // It starts as zero so that the last line can always increment.

  if (!result[date]) {

    result[date] = 0

  }

  // Increment the number of times we've seen this date by 1.

  result[date]++

}

​

console.log(result)