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Little improvements on npm commands + Upgrade of cross-env #2894

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cdae0ba
Improved daysInMonth performance
Genarito Jun 21, 2025
69295df
Fixed eslint command
Genarito Jun 21, 2025
7dc95ff
Added missing cross-env
Genarito Jun 21, 2025
b3ce7b8
Improved daysInMonth return type
Genarito Jun 21, 2025
aefb632
chore: update cross-env to version 5.2.1
Genarito Jun 21, 2025
b4fa774
Merge branch 'dev' into improve-days-in-month
iamkun Aug 28, 2025
b84cc49
Merge branch 'dev' into improve-days-in-month
Genarito Oct 4, 2025
4cae573
Reverts commits b3ce7b8e07d9961b1883d8c8de86dbd893aef4ff and cdae0ba4…
Genarito Oct 4, 2025
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2 changes: 1 addition & 1 deletion package-lock.json
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6 changes: 3 additions & 3 deletions package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -5,9 +5,9 @@
"main": "dayjs.min.js",
"types": "index.d.ts",
"scripts": {
"test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && TZ=America/Whitehorse npm run test-tz && npm run test-tz && jest",
"test": "cross-env TZ=Pacific/Auckland npm run test-tz && cross-env TZ=Europe/London npm run test-tz && cross-env TZ=America/Whitehorse npm run test-tz && npm run test-tz && jest",
"test-tz": "date && jest test/timezone.test --coverage=false",
"lint": "./node_modules/.bin/eslint src/* test/* build/*",
"lint": "eslint src/* test/* build/*",
"prettier": "prettier --write \"docs/**/*.md\"",
"babel": "cross-env BABEL_ENV=build babel src --out-dir esm --copy-files && node build/esm",
"build": "cross-env BABEL_ENV=build node build && npm run size",
Expand Down Expand Up @@ -58,7 +58,7 @@
"babel-core": "^7.0.0-bridge.0",
"babel-jest": "^22.4.3",
"babel-plugin-external-helpers": "^6.22.0",
"cross-env": "^5.1.6",
"cross-env": "^5.2.1",
"eslint": "^4.19.1",
"eslint-config-airbnb-base": "^12.1.0",
"eslint-plugin-import": "^2.10.0",
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25 changes: 24 additions & 1 deletion src/index.js
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Expand Up @@ -6,6 +6,22 @@ let L = 'en' // global locale
const Ls = {} // global loaded locale
Ls[L] = en

/** Index to get the number of days */
const MONTH_DAYS = {
0: 31, // January
1: 28, // February
2: 31, // March
3: 30, // April
4: 31, // May
5: 30, // June
6: 31, // July
7: 31, // August
8: 30, // September
9: 31, // October
10: 30, // November
11: 31 // December
}

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@iamkun iamkun Aug 28, 2025

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Introducing the MONTH_DAYS constant might increase the bundle size, which may not be an ideal optimization?

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@Genarito Genarito Aug 30, 2025

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Hi @iamkun, if you prefer, I can roll back this change. But with minification, it compresses to roughly:

const MONTH_DAYS={0:31,1:28,2:31,3:30,4:31,5:30,6:31,7:31,8:30,9:31,10:30,11:31}

That’s 80 bytes. After gzip compression, it’s 70 bytes (source).

So in practice, this code would increase the bundle size by 0.07 KB (virtually negligible).

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@iamkun iamkun Sep 1, 2025

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I've noticed this PR introduces some additional code into both utils and index.

A core principle of Day.js is its minimal bundle size, and we're highly sensitive to any changes that might increase it. For a change like this to be a worthwhile trade-off, we would need to see a significant performance improvement over the current endOf implementation.

Have you conducted any performance benchmarks to demonstrate the gains of this new approach? This data would be very helpful for us to evaluate if the change is a net positive for the project.

Looking forward to your thoughts!

const IS_DAYJS = '$isDayjsObject'

// eslint-disable-next-line no-use-before-define
Expand Down Expand Up @@ -389,7 +405,14 @@ class Dayjs {
}

daysInMonth() {
return this.endOf(C.M).$D
const numberOfDays = MONTH_DAYS[this.$M]

// February (leap year)
if (this.$M === 1 && U.yearIsLeap(this.$y)) {
return numberOfDays + 1
}

return numberOfDays
}

$locale() { // get locale object
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4 changes: 3 additions & 1 deletion src/plugin/isLeapYear/index.js
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
import U from '../../utils'

export default (o, c) => {
const proto = c.prototype
proto.isLeapYear = function () {
return ((this.$y % 4 === 0) && (this.$y % 100 !== 0)) || (this.$y % 400 === 0)
return U.yearIsLeap(this.$y)
}
}

5 changes: 4 additions & 1 deletion src/utils.js
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Expand Up @@ -45,11 +45,14 @@ const prettyUnit = (u) => {

const isUndefined = s => s === undefined

const yearIsLeap = year => ((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)

export default {
s: padStart,
z: padZoneStr,
m: monthDiff,
a: absFloor,
p: prettyUnit,
u: isUndefined
u: isUndefined,
yearIsLeap
}
2 changes: 1 addition & 1 deletion types/index.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -329,7 +329,7 @@ declare namespace dayjs {
* ```
* Docs: https://day.js.org/docs/en/display/days-in-month
*/
daysInMonth(): number
daysInMonth(): 28 | 29 | 30 | 31
/**
* To get a copy of the native `Date` object parsed from the Day.js object use `dayjs#toDate`.
* ```
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