From 22178822818eadfdbea2807e35027aa3f23a4a3b Mon Sep 17 00:00:00 2001
From: Frank Lin <github@linshuang.info>
Date: Sun, 6 Sep 2026 21:59:32 -0700
Subject: [PATCH] Fix identity-entry filter miscounting non-BMP characters as
 multi-char
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

k.length counts UTF-16 code units, so a single character above U+FFFF
(e.g. 𪙏) reports length 2 and its self-mapping entry survives the
"char => same char" filter meant to trim redundant dictionary rows.
Switch to a code-point count via [...k].length.

Fixes #49
---
 CHANGELOG.md | 6 ++++++
 build.js     | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4caae0e..e78e2a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,12 @@
 
 All notable changes to this project will be documented in this file.
 
+## Unreleased
+
+### Fixed
+
+- Fix the dictionary build script incorrectly keeping redundant "character maps to itself" entries for characters outside the Basic Multilingual Plane (e.g. 𪙏), since `String.prototype.length` counts UTF-16 code units rather than code points. These entries are now correctly filtered out, slightly reducing dictionary size with no effect on conversion results. ([#49](https://github.com/nk2028/opencc-js/issues/49), reported by [@obxyann](https://github.com/obxyann), thanks!)
+
 ## 1.4.2 - 2026-08-22
 
 ### Changed
diff --git a/build.js b/build.js
index 0398b78..5be2963 100644
--- a/build.js
+++ b/build.js
@@ -126,7 +126,7 @@ function loadFile(fileName) {
   if (!fileContentCache[fileName]) {
     fileContentCache[fileName] = getEntries(fileName)
       .map(([k, values]) => [k, values[0]]) // only select the first candidate, the subsequent candidates are ignored
-      .filter(([k, v]) => k !== v || k.length > 1) // remove “char => the same char” convertions to reduce file size
+      .filter(([k, v]) => k !== v || [...k].length > 1) // remove “char => the same char” convertions to reduce file size
       .map(([k, v]) => k + ' ' + v)
       .join('|');
     const outputFile = getAbsPath(`./dist/esm-lib/dict/${fileName}.js`);