Examine if a Day stands in JavaScript

Aug 14, 2023.

In JavaScript, a day is void if its valueOf() is NaN

 const day =  brand-new  Day( NaN);.
date.toString(); 

This is challenging due to the fact that day still resembles a legitimate day: it is still instanceof Day, and so on.
One means to look for an “Void Day” is to inspect if the day’s valueOf() is NaN:

 Number isNaN( date.valueOf());.

 const validDate =  brand-new  Day(' 2022-06-01');.
 Number isNaN( validDate.valueOf()); 

Debugging Why a Day is Void

There are 2 typical factors for an “Void Day”.
The initial is passing a worth that JavaScript can not take a day to the brand-new Day() contractor as adheres to.

 const badDate =  brand-new  Day(' foobar');.
badDate.valueOf();.
badDate.toString(); 

Void day strings aren’t the only prospective reason: coming on a numerical computation that amounts to NaN additionally creates “Void Day”.

 const obj = {};.


 const badDate2 =  brand-new  Day( 3 * obj.nonexistentProperty);.
badDate2.valueOf();.
badDate2.toString(); 

A legitimate day can come to be a void day because of day control techniques like setDate() and also setHours() As an example:

 const obj = {};.

 const badDate3 =  brand-new  Day(' 2023-06-01');.

badDate3.setHours( 3 * obj.nonexistentProperty);.
badDate3.valueOf();.
badDate3.toString(); 

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