[ksa]

const day = (new Date()).getDay();
            let html = '<p>INFORMATION</p>';
            if (day == 1) html = '1.dat';
			if (day == 2) html = '2.dat';			
			if (day == 3) html = '3.dat'; 
			if (day == 4) html = '4.dat';
			if (day == 5) html = '5.dat';
			if (day == 6) html = '6.dat';
			if (day == 7) html = '7.dat';
//...

Хорош индусить.

const day = (new Date()).getDay();
let html = '<p>INFORMATION</p>';
if (day) html = day + '.dat';
alert(html)