From 85604f98063cdf3263ecac013544af4a6a441bd3 Mon Sep 17 00:00:00 2001
From: koding88 <duongngocanh2k03@gmail.com>
Date: Mon, 24 Aug 2026 23:04:37 +0700
Subject: [PATCH] fix(core): treat mixed-case ms unit as millisecond instead of
 minute

prettyUnit consulted the special map before lowercasing, then
stripped a trailing 's', so 'MS'/'Ms'/'mS' resolved to the string
'm'. Consequences while every other unit was case-insensitive:

- get('MS') threw TypeError (this.m is not a function)
- set('MS', n) was a silent no-op
- startOf/endOf('MS') were clone-only no-ops

Look up the special map again after lowercasing so mixed-case ms
behaves exactly like 'ms'.
---
 src/utils.js         | 3 ++-
 test/get-set.test.js | 9 +++++++++
 test/utils.test.js   | 3 +++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/utils.js b/src/utils.js
index 324bc5e11..f3e4c20b3 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -40,7 +40,8 @@ const prettyUnit = (u) => {
     ms: C.MS,
     Q: C.Q
   }
-  return special[u] || String(u || '').toLowerCase().replace(/s$/, '')
+  const lower = String(u || '').toLowerCase()
+  return special[u] || special[lower] || lower.replace(/s$/, '')
 }
 
 const isUndefined = s => s === undefined
diff --git a/test/get-set.test.js b/test/get-set.test.js
index dae4d476c..23b04bebd 100644
--- a/test/get-set.test.js
+++ b/test/get-set.test.js
@@ -64,6 +64,15 @@ it('Millisecond', () => {
   expect(dayjs().millisecond()).toBe(moment().millisecond())
   expect(dayjs().millisecond(0).valueOf()).toBe(moment().millisecond(0).valueOf())
   expect(dayjs().millisecond(1).valueOf()).toBe(moment().millisecond(1).valueOf())
+  expect(dayjs().get('MS')).toBe(dayjs().get('ms'))
+})
+
+it('Set Millisecond with short and mixed-case units', () => {
+  const d = dayjs('2024-06-15T12:34:56.789')
+  expect(d.get('MS')).toBe(789)
+  expect(d.set('MS', 500).millisecond()).toBe(500)
+  expect(d.set('Ms', 250).millisecond()).toBe(250)
+  expect(d.startOf('MS').valueOf()).toBe(d.startOf('ms').valueOf())
 })
 
 it('Set Day', () => {
diff --git a/test/utils.test.js b/test/utils.test.js
index 0d7e6e044..d40ebc36a 100644
--- a/test/utils.test.js
+++ b/test/utils.test.js
@@ -18,6 +18,9 @@ it('PrettyUnit', () => {
   expect(prettyUnit('m')).toBe('minute')
   expect(prettyUnit('s')).toBe('second')
   expect(prettyUnit('ms')).toBe('millisecond')
+  expect(prettyUnit('MS')).toBe('millisecond')
+  expect(prettyUnit('Ms')).toBe('millisecond')
+  expect(prettyUnit('mS')).toBe('millisecond')
   expect(prettyUnit('Q')).toBe('quarter')
   expect(prettyUnit()).toBe('')
 })