const
m
=
moment
();
// now
m
.
add
(
3
,
'days'
);
// m is now three days in the future
m
.
subtract
(
2
,
'years'
);
// m is now two years minus three days in the past
m
=
moment
();
// reset
m
.
startOf
(
'year'
);
// m is now Jan 1 of this year
m
.
endOf
(
'month'
);
// m is now Jan 31 of this year
Moment.js also allows you to chain methods:
const
m
=
moment
()
.
add
(
10
,
'hours'
)
.
subtract
(
3
,
'days'
)
.
endOf
(
'month'
);
// m is the end of the month you would be in if you
// traveled 10 hours into the future then 3 days back
User-Friendly Relative Dates
Very often, it’s nice to be able to present date information in a relative fashion: “three
days ago” as opposed to a date. Moment.js makes this easy:
moment
().
subtract
(
10
,
'seconds'
).
fromNow
();
// a few seconds ago
moment
().
subtract
(
44
,
'seconds'
).
fromNow
();
// a few seconds ago
moment
().
subtract
(
45
,
'seconds'
).
fromNow
();
// a minute ago
moment
().
subtract
(
5
,
'minutes'
).
fromNOw
();
// 5 minutes ago
moment
().
subtract
(
44
,
'minutes'
).
fromNOw
();
// 44 minutes ago
moment
().
subtract
(
45
,
'minutes'
).
fromNOw
();
// an hour ago
moment
().
subtract
(
5
,
'hours'
).
fromNOw
();
// 4 hours ago
moment
().
subtract
(
21
,
'hours'
).
fromNOw
();
// 21 hours ago
moment
().
subtract
(
22
,
'hours'
).
fromNOw
();
// a day ago
moment
().
subtract
(
344
,
'days'
).
fromNOw
();
// 344 days ago
moment
().
subtract
(
345
,
'days'
).
fromNOw
();
// a year ago
As you can see, Moment.js has chosen some arbitrary (but reasonable) breakpoints
for when to switch to displaying a different unit. It’s a handy way to get user-friendly
relative dates.
Conclusion
If you take away three things from this chapter, they should be the following:
• Internally, dates are represented as the number of milliseconds from the Unix
Epoch (Jan 1, 1970 UTC).
• Be aware of the time zone when you’re constructing dates.
• If you want sophisticated date formatting, consider Moment.js.
User-Friendly Relative Dates | 227
