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Comparing 2 dates is something we’ve to do often in a JavaScript app.
In this article, we’ll look at how to compare 2 dates with JavaScript.
Comparing Timestamps
One easy way to compare 2 dates is to compare their timestamps.
We can get the timestamp with the getTime
method.
For instance, we can write:
const d1 = new Date();
const d2 = new Date(d1);
const same = d1.getTime() === d2.getTime();
const notSame = d1.getTime() !== d2.getTime();
getTime
returns the UNIX epoch in seconds.
It’s time number of seconds since January 1, 1970 midnight UTC.
We can also write:
const d1 = new Date();
const d2 = new Date(d1);
const same = +d1 === +d2;
const notSame = +d1 !== +d2;
which replaces getTime
with the +
before the date objects.
It does the same thing as getTime
.
Relational Operators
We can use relational operators directly with date objects.
For instance, we can write:
const d1 = new Date(2021, 0, 1);
const d2 = new Date(2021, 0, 2);
d1 < d2;
d1 <= d2;
d1 > d2;
d1 >= d2;
to compare them directly with the relational operators.
d1
and d2
will be converted to timestamps before comparing.
Subtracting Dates
We can also subtract one date from another and compare the result to what we want.
For instance, we can write:
const d1 = new Date(2021, 0, 1);
const d2 = new Date(2021, 0, 2);
console.log(d1 - d2 === 0);
console.log(d1 - d2 < 0);
console.log(d1 - d2 > 0);
This works because d1
and d2
are converted to timestamps before we subtract them.
Comparing Year, Month, and Date
We can compare the year, month, and day of 2 date objects to check if they’re the same to determine if they’re the same date.
For instance, we can write:
const d1 = new Date(2021, 0, 1);
const d2 = new Date(2021, 0, 2);
const isSameDate = d1.getFullYear() === d2.getFullYear() &&
d1.getDate() === d2.getDate() &&
d1.getMonth() === d2.getMonth();
getFullYear
returns the 4 digit year number.
getDate
returns the date.
And getMonth
returns the month from 0 to 11. 0 is January, 1 is February, etc.
Conclusion
We can compare 2 dates easily with JavaScript by converting them to numbers with various operators.
Then we can compare them.
We can also compare their year, month, and day values individually.
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