BetterDate

BetterDate is a JavaScript class just like the built-in Date, except:

• Numeric month values are one-indexed like year and date (there is no year, month, or day zero), instead of zero-indexed.
• Values can be modified with relative values using add* functions, instead of being absolute requiring both a set* and get* to be called to modify by a delta.
• The time zone offset is modifiable, instead of being unmodifiable without modifying the interpretor's environment.
• The time zone name is accessible as a separate property and is modifiable, instead of being, inaccessible and unmodifiable without modifying the interpretor's environment.
• Week of the year information is accessible (as a fractional week, Math.floor the result for whole weeks or Math.ceil the result for ordinal/partial weeks).
• Leap year information is available on instances for the year represented and on the class for any year in question.
• Day of the week is still zero-indexed.

let betterDate = new BetterDate();

The '1' is one-indexed to intuitively mean 'January', not zero-indexed to mean 'February'.

betterDate = new BetterDate( 2017, 1, 26 );
new Date( betterDate );
// Thu Jan 26 2017 00:00:00 GMT-0600 (Central Standard Time)

Remove 10 hours from a 'BetterDate':

let epoch_ms = betterDate.addHours( -10 );
// 1485374400000
betterDate.toString();
// Wed Jan 25 2017 14:00:00 GMT-0600 (Central Standard Time)

Change the time zone offset (and name) without affecting the represented time.

betterDate.setTimezoneOffset( 480 );
betterDate.setTimezoneName( 'America/Los_Angeles' );
betterDate.toString();
// Wed Jan 25 2017 12:00:00 GMT-0800 (America/Los_Angeles)
new Date( betterDate );
// Wed Jan 25 2017 14:00:00 GMT-0600 (Central Standard Time)

Get week of year.

Math.ceil( betterDate.getWeeksOfYear());
// 4