js is a simple instance of determining whether a set of dates is contiguous

This is a question asked by a friend in the group. At that time, I said it was enough to judge whether day was adjacent. Later, after careful consideration, I found that it was completely wrong.

Problem demand

Given five dates in the same format, how can we judge whether they are five consecutive days?

At that time, I sorted after the first reaction getDay (), and then compared it before and after. .

But if you think about it carefully, it is totally wrong, for example, this week's 1 and next week's 2, which will also misjudge.

Moreover, it is not only such a problem, but also such problems as cross-month, cross-year and leap month.

Then you have the following code.

Let the timestamp be smoothed out by 1 cut

In order not to entangle these problems, I thought of timestamps, which can completely ignore the above problems, as long as the timestamps are processed and finally compared.

Then I gave the following code:

let days = [
 '2016-02-28',
 '2016-02-29', //  Leap month 
 '2016-03-01', //  Cross-moon 
 '2016-03-02',
 '2016-03-03',
]

//  Sort first, then turn to timestamp 
let _days = days.sort().map((d, i) => {
 let dt = new Date(d)
 dt.setDate(dt.getDate() + 4 - i) //  Process to the same date 

 return +dt
})

//  Compare whether timestamps 1 To 
console.log(
 _days[0] == _days[1] &&
 _days[0] == _days[2] &&
 _days[0] == _days[3] &&
 _days[0] == _days[4]
)

All the problems of ok 1 have been solved, and it doesn't matter whether it is a new year, a month or a leap month.

Universal function encapsulation

The above code is still a little flawed, because the minutes and seconds are not processed, and if sometimes the minutes and seconds are erased first.

let days = [
 '2016-02-28 12:00:00',
 '2016-02-29 12:00:01', //  Leap month 
 '2016-03-01 12:00:02', //  Cross-moon 
 '2016-03-02 12:00:03',
 '2016-03-03 12:00:04',
 '2016-03-04 12:00:04',
]

console.log(continueDays(days))

function continueDays(arr_days) {
 //  Sort first, then turn to timestamp 
 let days = arr_days.sort().map((d, i) => {
  let dt = new Date(d)
  dt.setDate(dt.getDate() + 4 - i) //  Process to the same date 

  //  Erase   Hour   Points   Seconds   Milliseconds 
  dt.setHours(0)
  dt.setMinutes(0)
  dt.setSeconds(0)
  dt.setMilliseconds(0)

  return +dt
 })

 let ret = true

 days.forEach(d => {
  if (days[0] !== d) {
   ret = false
  }
 })

 return ret
}

This function only changed 2 places, erase time, second, millisecond and loop comparison, and everything else is 1.

Summary

js processing time is very simple, such as writing a date plug-in. In fact, it is very easy to realize with Date, but you need to know api of Date.

Of course, to say simple, or php is the simplest, which is simply against the sky.