kevinius - 1 year ago 85
Javascript Question

# Check if a date is "tomorrow" or "the day after tomorrow"

I'm looking for a way to get "tomorrow" and "the day after tomorrow" returned from a function that receives to dates:

The current date:

"2015/04/24 18:15:00"

The date in the future:

"2015/04/25 02:40:00"

The function should return "tomorrow" here. I tried looking up some functions but they all return 0 not 1.

``````function days_between(date1, date2) {

// The number of milliseconds in one day
var ONE_DAY = 1000 * 60 * 60 * 24

// Convert both dates to milliseconds
var date1_ms = date1.getTime()
var date2_ms = date2.getTime()

// Calculate the difference in milliseconds
var difference_ms = Math.abs(date1_ms - date2_ms)

// Convert back to days and return
return Math.round(difference_ms/ONE_DAY)

}
``````

Any ideas?

First, here's the documentation on the Javascript Date object and its prototype.

So, how can you determine if a particular day (`date2`) is one day after another (`date1`)? Well, add one day to `date1` and see if the dates match:

``````var date1_tomorrow = new Date(date1.getFullYear(), date1.getMonth(), date1.getDate() + 1);
if (date1_tomorrow.getFullYear() == date2.getFullYear() && date1_tomorrow.getMonth() == date2.getMonth() && date1_tomorrow.getDate() == date2.getDate()) {
return "tomorrow"; // date2 is one day after date1.
}
``````

If you want to determine if `date2` is two days after `date1`, you can use the same logic as above but add 2 days instead of 1:

``````var date1_overmorrow = new Date(date1.getFullYear(), date1.getMonth(), date1.getDate() + 2);
if (date1_overmorrow.getFullYear() == date2.getFullYear() && date1_overmorrow.getMonth() == date2.getMonth() && date1_overmorrow.getDate() == date2.getDate()) {
return "the day after tomorrow"; // date2 is two days after date1.
}
``````

If the dates are not 1 or 2 days apart, the final bit would be to just return the date in your desired format:

``````return date2.toLocaleString(); // Firefox 29+, Chrome 24+, IE 11+
// OR
return date2.getFullYear() + '/' + (date2.getMonth() + 1) + '/' + date2.getDate() + ' ' + date2.getHours() + ':' + date2.getMinutes() + ':' + date2.getSeconds(); // Et al.
``````

# Test

``````function incrementDate(date, n) {
return new Date(date.getFullYear(), date.getMonth(), date.getDate() + n);
}

function compareDates(date1, date2) {
return date1.getFullYear() == date2.getFullYear() && date1.getMonth() == date2.getMonth() && date1.getDate() == date2.getDate();
}

\$(function() {
var \$output = \$('#output');

var comparisons = [
{'start': new Date(2016, 6 - 1, 1), 'inc': 1, 'target': new Date(2016, 6 - 1, 2)},
{'start': new Date(2016, 6 - 1, 30), 'inc': 1, 'target': new Date(2016, 7 - 1, 1)},
{'start': new Date(2016, 12 - 1, 31), 'inc': 1, 'target': new Date(2017, 1 - 1, 1)}
];
for (var i = 0, len = comparisons.length; i < len; i += 1) {
var comp = comparisons[i];
var \$row = \$('<tr>');

\$('<td>').text(comp.start.toString()).appendTo(\$row);
\$('<td>').text(comp.inc).appendTo(\$row);
\$('<td>').text(comp.target.toString()).appendTo(\$row);
\$('<td>').text(compareDates(comp.target, incrementDate(comp.start, comp.inc)) ? 'yes' : 'no').appendTo(\$row);

\$output.append(\$row);
}
});``````
``````<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<table>