It is very simple, that you might not need a library, although there are cautions.
That is, using Date object. Be aware of months and leap years. Don't try to use straight simple approximation of raw milliseconds.
Natively adding numbers, e.g. days, months, to Date object
type Unit = "ms" | "s" | "min" | "h" | "d" | "w" | "mo" | "y";
const addDate: Record<Unit, (d: Date, n: number) => Date> = {
ms: (d, n) => {
d.setMilliseconds(d.getMilliseconds() + n);
return new Date(d);
},
s: (d, n) => {
d.setSeconds(d.getSeconds() + n);
return new Date(d);
},
min: (d, n) => {
d.setMinutes(d.getMinutes() + n);
return new Date(d);
},
h: (d, n) => {
d.setHours(d.getHours() + n);
return new Date(d);
},
d: (d, n) => {
d.setDate(d.getDate() + n);
return new Date(d);
},
w: (d, n) => {
d.setDate(d.getDate() + n * 7);
return new Date(d);
},
mo: (d, n) => {
d.setMonth(d.getMonth() + n);
return new Date(d);
},
y: (d, n) => {
d.setFullYear(d.getFullYear() + n);
return new Date(d);
},
};
Adding number to Date is not that hard. Just remember to refresh the Date object, by cloning new Date(d).
Principles of calculating Duration
- First, plan for appropriate Date component mapping -
Record<Unit, number> - Second, mitigate negatives
parse(
current: (d: Date) => number,
upper?: {
get: (d: Date) => number;
set: (d: Date, v: number) => void;
inc: (d: Date) => number;
}
) {
let a = current(this.dates[1]) - current(this.dates[0]);
if (upper) {
while (a < 0) {
a += upper.inc(this.dates[0]);
upper.set(this.dates[1], upper.get(this.dates[1]) - 1);
this.dates[1] = new Date(this.dates[1]);
}
}
return a;
}
Now, the problem here is that you will need to account for leap years.
inc: (d) => {
const y = d.getFullYear();
let isLeapYear = true;
if (y % 4) {
isLeapYear = false;
} else if (y % 100) {
isLeapYear = true;
} else if (y % 400) {
isLeapYear = false;
}
return [
31, // Jan
isLeapYear ? 29 : 28, // Feb
31, // Mar
30, // Apr
31, // May
30, // Jun
31, // Jul
31, // Aug
30, // Sep
31, // Oct
30, // Nov
31, // Dec
][d.getMonth()];
},
Note that .getMonth() is zero-indexed, i.e. January is 0, December is 11.
Weeks need to be calculated separately.
const w = Math.floor(d / 7);
d = d % 7;
Constructing an ordered Record, removing unnecessity, and joining to a useful string
const m = durationToRecord(from, to);
const str = Object.entries(m.d)
.filter(([, v]) => v)
.reverse()
.slice(0, trim)
.map(([k, v]) => `${v.toLocaleString()}${unit[k as Unit] || k}`)
.join(" ");
Testing
I made it cursorly, so I don't even bother installing ts-mocha or jest-ts.
const maxAcceptable: Partial<Record<Unit, number>> = {
ms: 1000,
s: 60,
min: 60,
h: 24,
d: 31,
w: 4,
mo: 12,
};
const now = new Date();
/**
* 10k repeats
*/
Array(10000)
.fill(null)
.map(() => {
/**
* From minutes to about 20 years' duration
*/
Array.from(Array(8), (_, i) => (Math.random() + 0.1) * 10 ** (i + 5)).map((n) => {
const to = new Date(+now + n);
console.log(
durationToString(now, to, {
sign: false,
trim: 2,
})
);
const map = durationToRecord(now, to);
Object.entries(map.d).map(([k, v]) => {
const max = maxAcceptable[k as Unit];
if (max && v > max) {
console.error({ k, v, map });
throw new Error("Some value exceeded the limit");
}
});
const calculated = Object.entries(map.d).reduce(
(prev, [k, v]) => addDate[k as Unit](prev, v),
new Date(now)
);
const ratio = (+calculated - +now) / n;
if (ratio < 0.95 || ratio > 1.05) {
console.error({ now, to, calculated, map });
throw new Error("Duration might be miscalculated (CI 95%)");
}
});
});
Indeed, a more correct way would be to use ISO date-time string, and remove smallest parts. I have tried it, and sometimes I missed by 1 day.
Fine tuning
export function humanizeDurationToNow(epoch: number) {
const now = new Date();
const msec = +now - epoch;
if (msec < 5000) {
return 'Just posted';
}
return durationToString(new Date(epoch), now, { trim: 2 }) + ' ago';
}
Real code
The real code can be found on GitHub and NPM. It uses absolutely zero dependencies.
Top comments (1)
A bug found.
It is never more than one day. Two days or more never.
The problem is, what is the real cause, why error is never more than 1 DAY, nor in other units?
Qualm is this code.
So, I reposted on Hashnode, starting with "bug"