### Using [ES6 Array Initializer][1]

You can [get the number of days in a specified month][2], and then create a new array with that length and each of the days as items.

```js
const getAllDaysInMonth = (month, year) =>
  Array.from(
    { length: new Date(year, month, 0).getDate() },
    (_, i) => new Date(year, month - 1, i + 1)
  );
```

### Demo in Stack Snippets





    const getAllDaysInMonth = (month, year) =>
      Array.from(
        {length: new Date(year, month, 0).getDate()}, // get next month, zeroth's (previous) day
        (_, i) => new Date(year, month - 1, i + 1)    // get current month (0 based index)
      );

    const allDatesInOctober = getAllDaysInMonth(10, 2021)

    console.log(allDatesInOctober.map(x => x.toLocaleDateString([], { month: "short", day: "numeric" })))

    // ['Oct 1', 'Oct 2', 'Oct 3', 'Oct 4', 'Oct 5', 'Oct 6', 'Oct 7', 'Oct 8', 'Oct 9', 'Oct 10', 'Oct 11', 'Oct 12', 'Oct 13', 'Oct 14', 'Oct 15', 'Oct 16', 'Oct 17', 'Oct 18', 'Oct 19', 'Oct 20', 'Oct 21', 'Oct 22', 'Oct 23', 'Oct 24', 'Oct 25', 'Oct 26', 'Oct 27', 'Oct 28', 'Oct 29', 'Oct 30', 'Oct 31']




  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from#sequence_generator_range
  [2]: https://stackoverflow.com/q/1184334/1366033

is there a way to have all the days of a month or of a year? I am looking for this in order to disable some specific days in a datepicker, i would have a page in the back-office to select these days to disable. 

So i would need to show all the days in a month, and add a "activate or deactive" button below each day. Is there a way to find these days with the Date object? I found this link for example : https://stackoverflow.com/questions/6729497/displaying-all-the-days-of-a-month but i don't really understand it, plus it is Java, i am trying to find a solution in javascript.

Thank you for your help


Find all the days in a month with Date object?

There are several functions available in T-SQL under the [Conversion][1] category, all of which have variants prefixed with `TRY_` which:

> Returns a value cast to the specified data type if the cast succeeds; otherwise, returns null.


* [`CAST`][2] / [`TRY_CAST`][4]
* [`CONVERT`][2] / [`TRY_CONVERT`][5]
* [`PARSE`][3] / [`TRY_PARSE`][6]

You can use them like this:

```sql
SELECT TRY_CAST('2020-05-27' AS DATE)
SELECT TRY_CONVERT(DATE, '2020-05-27')
SELECT TRY_PARSE('2020-05-27' AS DATE)
```



[1]: https://learn.microsoft.com/en-us/sql/t-sql/functions/conversion-functions-transact-sql
[2]: https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-ver15
[3]: https://learn.microsoft.com/en-us/sql/t-sql/functions/parse-transact-sql?view=sql-server-ver15
[4]: https://learn.microsoft.com/en-us/sql/t-sql/functions/try-cast-transact-sql?view=sql-server-ver15
[5]: https://learn.microsoft.com/en-us/sql/t-sql/functions/try-convert-transact-sql?view=sql-server-ver15
[6]: https://learn.microsoft.com/en-us/sql/t-sql/functions/try-parse-transact-sql?view=sql-server-ver15

I have the following code in a stored procedure in MSSQL Transact:

    CAST(CONVERT(Datetime, aof.Transactiondate) AS date)

aof.Transactiondate is a varchar(8) and should be written in the form of '20160202' or '20160117'.
Today I found out that in rare instances aof.Transactiondate can be a '1' and thus my code crashes completely.

Can I do anything to make sure that the above don't crash and sets a defult date or something instead of crashing??

Theoretically I could make sure that there is 8 chars in the varchar and then seperate the char into 4, 2 and 2 block and finally make sure that block one is between 2015 and 2016 (only relevant at the moment), second block is between 1 and 12 and third block is between 1 and 31 but that seems to be a huge amount of work.

Safe convert from string to date in Transact

You don't need string manipulation to get a DateTime without the time part, just use [DateTime.Date](https://msdn.microsoft.com/en-us/library/system.datetime.date(v=vs.110).aspx). 

To get the time span between two dates, just subtract one from the other. Subtracting one date from another returns a [TimeSpan](https://msdn.microsoft.com/en-us/library/system.timespan(v=vs.110).aspx) object whose [Days](https://msdn.microsoft.com/en-us/library/system.timespan.days(v=vs.110).aspx) property is the difference in full dates.

All you need to do is :

    Dim days As Integer =(date2.Date-date1.Date).Days 

This way you avoid generating and parsing temporary strings.



The [`DateDiff`][1] function reports Day Intervals on a 24 hour basis, which provides an odd result when asking how many days ago something happened when the time of day changes.

For example, if I want to get the number of days since yesterday afternoon, if it hasn't been a full 24 hours, DateDiff will return `0`, whereas most of the time I ask that question, I'm expecting yesterday to be treated as 1 day ago, regardless of timestamp.

Is there a way to get DateDiff to return the number of calendar days?

### [Demo in .NET Fiddle][2]



	Dim date1 As DateTime = #3/1/2017 5:00 PM#
	Dim date2 As DateTime = #3/2/2017 10:00 AM#
	
	Dim daysAgo = DateDiff(DateInterval.Day, date1, date2)
	Dim msg = String.Format("Last date was {0} day(s) ago on {1}. ", daysAgo, date1.ToShortDateString())
	Console.WriteLine(msg) ' Last date was 0 day(s) ago on 3/1/2017. 

The following questions on StackOverflow do not address this nuance:

* [Get date difference in VB.NET][SO1]
* [Calculating Number of Months between 2 dates][SO2]
* [How to find the number of days between two dates / DateTimePickers][SO3] 


[1]: https://msdn.microsoft.com/en-us/library/ms127413.aspx
[2]: https://dotnetfiddle.net/sZdyMN

[SO1]: https://stackoverflow.com/q/20635037/1366033
[SO2]: https://stackoverflow.com/q/3249968/1366033
[SO3]: https://stackoverflow.com/q/19017466/1366033

Get calendar days between two dates

You could write something like this:

```js
function parseDate(dateString) {
  var dateParts = dateString.split("/"),
      years = dateParts[0],
      months = dateParts[1],
      days = dateParts[2]
  
  // sanity check date parts
  if (days > 31) return "Invalid Date - Days"
  if (months > 12) return "Invalid Date - Months"
  
  var myDate = new Date(years, months, days)
  
  return myDate
}
```

**Demo in Stack Snippets**





    function parseDate(dateString) {
      var dateParts = dateString.split("/"),
          years = dateParts[0],
          months = dateParts[1],
          days = dateParts[2]
      
      // sanity check date parts
      if (days > 31) return "Invalid Date - Days"
      if (months > 12) return "Invalid Date - Months"
      
      var myDate = new Date(years, months, days)
      
      return myDate
    }

    console.log('2020/05/15: ', parseDate('2020/05/15'))
    console.log('2020/05/99: ', parseDate('2020/05/99'))
    console.log('2020/05/100: ', parseDate('2020/05/100'))
    console.log('2020/70/1000: ', parseDate('2020/70/1000'))

IE11's `Date.parse` function "succeeds" on a large number of invalid dates.  

Without using a third-party library, what is the proper way to validate whether a string in the format `YYYY/MM/DD` contains an actual "legal" date (e.g. "2020/02/29" succeeds, but "2019/02/29" fails, etc) in javascript?

**[Examples from IE11 console][1]:**


```js
new Date(Date.parse('2020/05/99')     // Fri Aug 07 2020
new Date(Date.parse('2020/05/100')    // Sat Aug 08 20202
new Date(Date.parse('2020/05/1000')   // Wed Jan 25 2023
new Date(Date.parse('2020/69/800000') // Fri Dec 29 4215
new Date(Date.parse('2020/69/1000')   // Sat May 27 2028
new Date(Date.parse('2020/70/1000')   // Invalid Date
```

  [1]: https://i.stack.imgur.com/j0jzK.png
