From ddb7c0d26436b3aab88bb91c8944f0c2fc5db88e Mon Sep 17 00:00:00 2001
From: xiehuanyi <74809554+xiehuanyi@users.noreply.github.com>
Date: Sun, 11 Oct 2026 10:04:14 +0300
Subject: [PATCH] Capitalize complete Unicode code points

---
 packages/change-case/src/index.spec.ts | 28 ++++++++++++++++++++++++++
 packages/change-case/src/index.ts      |  9 ++++++---
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/packages/change-case/src/index.spec.ts b/packages/change-case/src/index.spec.ts
index 14152e8a..62b659ed 100644
--- a/packages/change-case/src/index.spec.ts
+++ b/packages/change-case/src/index.spec.ts
@@ -381,6 +381,34 @@ const tests: [string, Result, Options?][] = [
 ];
 
 describe("change case", () => {
+  it("capitalizes supplementary-plane letters as complete code points", () => {
+    const lower = "\u{10428}";
+    const upper = "\u{10400}";
+    for (const locale of [undefined, false] as const) {
+      expect(capitalCase(`${lower}foo bar`, { locale })).toEqual(
+        `${upper}foo Bar`,
+      );
+      expect(sentenceCase(`${lower}foo bar`, { locale })).toEqual(
+        `${upper}foo bar`,
+      );
+      expect(pascalCase(`${lower}foo bar`, { locale })).toEqual(
+        `${upper}fooBar`,
+      );
+      expect(camelCase(`foo ${lower}bar`, { locale })).toEqual(
+        `foo${upper}bar`,
+      );
+      expect(trainCase(`${lower}foo bar`, { locale })).toEqual(
+        `${upper}foo-Bar`,
+      );
+      expect(
+        pascalCase(`${lower}foo bar`, {
+          locale,
+          mergeAmbiguousCharacters: true,
+        }),
+      ).toEqual(`${upper}fooBar`);
+    }
+  });
+
   for (const [input, result, options] of tests) {
     it(input, () => {
       expect(camelCase(input, options)).toEqual(result.camelCase);
diff --git a/packages/change-case/src/index.ts b/packages/change-case/src/index.ts
index a84701f2..5d1b489d 100644
--- a/packages/change-case/src/index.ts
+++ b/packages/change-case/src/index.ts
@@ -232,7 +232,10 @@ function capitalCaseTransformFactory(
   lower: (input: string) => string,
   upper: (input: string) => string,
 ) {
-  return (word: string) => `${upper(word[0])}${lower(word.slice(1))}`;
+  return (word: string) => {
+    const [char0] = word;
+    return `${upper(char0)}${lower(word.slice(char0.length))}`;
+  };
 }
 
 function pascalCaseTransformFactory(
@@ -240,10 +243,10 @@ function pascalCaseTransformFactory(
   upper: (input: string) => string,
 ) {
   return (word: string, index: number) => {
-    const char0 = word[0];
+    const [char0] = word;
     const initial =
       index > 0 && char0 >= "0" && char0 <= "9" ? "_" + char0 : upper(char0);
-    return initial + lower(word.slice(1));
+    return initial + lower(word.slice(char0.length));
   };
 }