fix: account for wide CJK characters in setWidth() ch calculation

The setWidth() method used str.length to compute the ch-unit
width for the search input's min-width / width style properties.
This is incorrect for wide (full-width) Unicode characters such as
Japanese (Hiragana / Katakana), Chinese (CJK Ideographs), Korean
(Hangul), and fullwidth Latin forms -- each of these occupies 2ch in
a standard browser font yet was counted as only 1.

The result is that a Japanese placeholder like 'エリアを選択してください'
(12 characters -> 24ch wide) was only given 13ch of min-width, causing
the text to be clipped.

Fix: replace both .length calls in setWidth() with a new module-level
helper getStringWidth() that iterates the string's Unicode code points
and adds 2 for any character in a wide/fullwidth Unicode block (standard
wcwidth-style logic), and 1 for everything else.

Fixes #1216

src/scripts/components/input.ts

@@ -1,6 +1,46 @@
 import { ClassNames } from '../interfaces/class-names';
 import { PassedElementType, PassedElementTypes } from '../interfaces/passed-element-type';
 
+/**
+ * Returns the display width of a string in `ch` units.
+ * Wide characters (CJK, Hangul, fullwidth forms, etc.) count as 2,
+ * all other characters count as 1. This matches how browsers render
+ * these characters relative to the `ch` unit (width of '0').
+ */
+function getStringWidth(str: string): number {
+  let width = 0;
+  for (const char of str) {
+    const code = char.codePointAt(0) ?? 0;
+    /* eslint-disable no-mixed-operators */
+    if (
+      (code >= 0x1100 && code <= 0x115f) || // Hangul Jamo
+      code === 0x2329 ||
+      code === 0x232a ||
+      (code >= 0x2e80 && code <= 0x303e) || // CJK Radicals, Kangxi, CJK Symbols
+      (code >= 0x3041 && code <= 0x33bf) || // Hiragana, Katakana, Bopomofo, CJK Compat
+      (code >= 0x3400 && code <= 0x4dbf) || // CJK Extension A
+      (code >= 0x4e00 && code <= 0x9fff) || // CJK Unified Ideographs
+      (code >= 0xa000 && code <= 0xa4cf) || // Yi Syllables / Radicals
+      (code >= 0xa960 && code <= 0xa97f) || // Hangul Jamo Extended-A
+      (code >= 0xac00 && code <= 0xd7af) || // Hangul Syllables
+      (code >= 0xf900 && code <= 0xfaff) || // CJK Compatibility Ideographs
+      (code >= 0xfe10 && code <= 0xfe1f) || // Vertical Forms
+      (code >= 0xfe30 && code <= 0xfe6f) || // CJK Compatibility Forms
+      (code >= 0xff01 && code <= 0xff60) || // Fullwidth Latin / Punctuation
+      (code >= 0xffe0 && code <= 0xffe6) || // Fullwidth Signs
+      (code >= 0x1b000 && code <= 0x1b001) || // Kana Supplement
+      (code >= 0x20000 && code <= 0x2fffd) || // CJK Extension B–D
+      (code >= 0x30000 && code <= 0x3fffd) // CJK Extension E+
+    ) {
+      width += 2;
+    } else {
+      width += 1;
+    }
+    /* eslint-enable no-mixed-operators */
+  }
+  return width;
+}
+
 export default class Input {
   element: HTMLInputElement;
 
@@ -110,10 +150,13 @@ export default class Input {
    * value or input value
    */
   setWidth(): void {
-    // Resize input to contents or placeholder
+    // Resize input to contents or placeholder.
+    // Uses getStringWidth() instead of .length so that wide characters
+    // (CJK, Hangul, fullwidth forms, etc.) are counted as 2ch rather than 1ch,
+    // preventing placeholder text truncation for languages like Japanese.
     const { element } = this;
-    element.style.minWidth = `${element.placeholder.length + 1}ch`;
-    element.style.width = `${element.value.length + 1}ch`;
+    element.style.minWidth = `${getStringWidth(element.placeholder) + 1}ch`;
+    element.style.width = `${getStringWidth(element.value) + 1}ch`;
   }
 
   setActiveDescendant(activeDescendantID: string): void {