val(date) modifies passed date instance

[vfonic]

Hi,

I've just experienced this issue:

var time = date.toTimeString().split(' ')[0]; // get hour and minute (there are better ways to do this)
var sched = later.parse.recur().on(time).time();
var dayOfWeek = later.dayOfWeek.val(date); // NOTE this line might mess up your `date` instance

console.log(dayOfWeek); // 3
console.log(date); // { 2017-12-19T20:00:00.000Z dw: 3 }

The date instance got modified. Is this expected behavior? I continued using date below this code point and received errors. I expected that call to val() won't change my date instance.

It's because this line of code:

later/src/constraint/dayofweek.js

Lines 29 to 31 in 5d38cc3

	val: function(d) {
	return d.dw || (d.dw = later.date.getDay.call(d)+1);
	},